U.S. patent application number 13/938018 was filed with the patent office on 2014-01-16 for polishing method.
The applicant listed for this patent is EBARA CORPORATION. Invention is credited to Takeshi IIZUMI, Yoichi KOBAYASHI, Katsuhide WATANABE.
Application Number | 20140017824 13/938018 |
Document ID | / |
Family ID | 49914311 |
Filed Date | 2014-01-16 |
United States Patent
Application |
20140017824 |
Kind Code |
A1 |
IIZUMI; Takeshi ; et
al. |
January 16, 2014 |
POLISHING METHOD
Abstract
A method of polishing a substrate having a film is provided. The
method includes: performing polishing of the substrate in a
polishing section; transporting the polished substrate to a
wet-type film thickness measuring device prior to cleaning and
drying of the substrate; measuring a thickness of the film by the
wet-type film thickness measuring device; comparing the thickness
with a predetermined target value; and if the thickness has not
reached the predetermined target value, performing re-polishing of
the substrate in the polishing section prior to cleaning and drying
of the substrate.
Inventors: |
IIZUMI; Takeshi; (Tokyo,
JP) ; WATANABE; Katsuhide; (Tokyo, JP) ;
KOBAYASHI; Yoichi; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
EBARA CORPORATION |
Tokyo |
|
JP |
|
|
Family ID: |
49914311 |
Appl. No.: |
13/938018 |
Filed: |
July 9, 2013 |
Current U.S.
Class: |
438/16 ; 438/14;
438/17 |
Current CPC
Class: |
H01L 21/76819 20130101;
H01L 21/7684 20130101; H01L 21/31053 20130101; H01L 21/3212
20130101; H01L 21/67075 20130101; H01L 21/76224 20130101; B24B
37/042 20130101; H01L 22/12 20130101; H01L 21/67253 20130101; H01L
21/67092 20130101; H01L 21/30625 20130101; G01B 11/0625 20130101;
H01L 21/31055 20130101; H01L 22/20 20130101; G01B 7/105 20130101;
B24B 37/013 20130101; B24B 49/12 20130101; G01B 11/0683
20130101 |
Class at
Publication: |
438/16 ; 438/14;
438/17 |
International
Class: |
H01L 21/306 20060101
H01L021/306 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 10, 2012 |
JP |
2012-154975 |
Claims
1. A method of polishing a substrate having a film, said method
comprising: performing polishing of the substrate in a polishing
section; transporting the polished substrate to a wet-type film
thickness measuring device prior to cleaning and drying of the
substrate; measuring a thickness of the film by the wet-type film
thickness measuring device; comparing the thickness with a
predetermined target value; and if the thickness has not reached
the predetermined target value, performing re-polishing of the
substrate in the polishing section prior to cleaning and drying of
the substrate.
2. The method according to claim 1, further comprising: calculating
an additional polishing time that is necessary for the thickness to
reach the predetermined target value, wherein the re-polishing
process is a process of re-polishing the substrate for the
additional polishing time in the polishing section prior to
cleaning and drying of the substrate.
3. The method according to claim 1, further comprising: terminating
the polishing process before the thickness of the film reaches the
predetermined target value.
4. The method according to claim 1, wherein: the polishing process
comprises a process of bringing the substrate into sliding contact
with a polishing pad attached to a polishing table, while supplying
a polishing liquid onto the polishing pad; and the re-polishing
process comprises a process of bringing the substrate into sliding
contact with the polishing pad attached to the same polishing
table, while supplying a polishing liquid onto the polishing
pad.
5. The method according to claim 1, wherein: the polishing process
comprises a process of bringing the substrate into sliding contact
with a polishing pad attached to a polishing table, while supplying
a polishing liquid onto the polishing pad; and the re-polishing
process comprises a process of bringing the substrate into sliding
contact with a different polishing pad attached to a different
polishing table, while supplying a polishing liquid onto the
different polishing pad.
6. The method according to claim 1, further comprising: if the
thickness has reached the predetermined target value, cleaning and
drying the substrate.
7. The method according to claim 1, further comprising: spraying a
liquid onto a subsequent substrate when performing the re-polishing
process and/or measuring the thickness of the film.
8. The method according to claim 1, further comprising: calculating
a delay in a polishing start time of a subsequent substrate, the
delay being due to the re-polishing process; and adjusting a timing
of starting polishing of the subsequent substrate.
9. A method of polishing a substrate having a film, said method
comprising: polishing the substrate while measuring a thickness of
the film with a film thickness sensor; terminating polishing of the
substrate when a measured value of the thickness of the film,
obtained from the film thickness sensor, reaches a predetermined
value; transporting the polished substrate to a wet-type film
thickness measuring device; measuring a thickness of the film by
the wet-type film thickness measuring device; calibrating the film
thickness sensor based on the measured value of the thickness of
the film obtained from the film thickness sensor and a measured
value of the thickness of the film obtained from the wet-type film
thickness measuring device; polishing a subsequent substrate while
measuring a thickness of a film of the subsequent substrate with
the calibrated film thickness sensor; and terminating polishing of
the subsequent substrate when the thickness of the film reaches a
predetermined target value.
10. The method according to claim 9, wherein the film thickness
sensor is an optical film thickness sensor or an eddy current film
thickness sensor.
11. A method of polishing a substrate having a film, said method
comprising: performing polishing of the substrate in a polishing
section; transporting the polished substrate, with its surface wet,
to a wet-type film thickness measuring device; measuring a
thickness of the film by the wet-type film thickness measuring
device; comparing the thickness with a predetermined target value;
and if the thickness has not reached the predetermined target
value, performing re-polishing of the substrate in the polishing
section prior to cleaning and drying of the substrate.
12. The method according to claim 11, further comprising:
calculating an additional polishing time that is necessary for the
thickness to reach the predetermined target value, wherein the
re-polishing process is a process of re-polishing the substrate for
the additional polishing time in the polishing section prior to
cleaning and drying of the substrate.
13. The method according to claim 11, further comprising:
terminating the polishing process before the thickness of the film
reaches the predetermined target value.
14. The method according to claim 11, wherein: the polishing
process comprises a process of bringing the substrate into sliding
contact with a polishing pad attached to a polishing table, while
supplying a polishing liquid onto the polishing pad; and the
re-polishing process comprises a process of bringing the substrate
into sliding contact with the polishing pad attached to the same
polishing table, while supplying a polishing liquid onto the
polishing pad.
15. The method according to claim 11, wherein: the polishing
process comprises a process of bringing the substrate into sliding
contact with a polishing pad attached to a polishing table, while
supplying a polishing liquid onto the polishing pad; and the
re-polishing process comprises a process of bringing the substrate
into sliding contact with a different polishing pad attached to a
different polishing table, while supplying a polishing liquid onto
the different polishing pad.
16. The method according to claim 11, further comprising: if the
thickness has reached the predetermined target value, cleaning and
drying the substrate.
17. The method according to claim 11, further comprising: spraying
a liquid onto a subsequent substrate when performing the
re-polishing process and/or measuring the thickness of the
film.
18. The method according to claim 11, further comprising:
calculating a delay in a polishing start time of a subsequent
substrate, the delay being due to the re-polishing process; and
adjusting a timing of starting polishing of the subsequent
substrate.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This document claims priority to Japanese Patent Application
No. 2012-154975, filed Jul. 10, 2012, the entire contents of which
are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a method of polishing a
substrate, such as a wafer, and more particularly to a polishing
method including the steps of measuring a film thickness of the
substrate after polishing it and re-polishing the substrate if the
film thickness has not reached a target value.
[0004] 2. Description of the Related Art
[0005] Semiconductor devices are expected to become finer and finer
in the future. In order to realize such a fine structure, a
polishing apparatus, which is typified by a CMP apparatus, is
required to have a more precise processing controllability and a
high polishing performance. Specifically, a more accurate remaining
film control (i.e., more accurate detection of a polishing end
point) and improved polishing results (i.e., less defects and high
planarity of polished surface) are required. In addition, a higher
productivity (i.e., throughput) is also required.
[0006] In the present polishing apparatus, so-called "rework",
which is re-polishing of the wafer, may be performed in order to
improve the polishing accuracy. This re-polishing includes the
steps of transporting the wafer, which has been polished in the
polishing apparatus, to an external film thickness measuring
device, measuring a film thickness of the polished wafer by the
film thickness measuring device, and polishing the wafer again in
order to eliminate a difference between the measured film thickness
and a target film thickness.
[0007] Flow of a conventional wafer polishing method will be
described with reference to FIG. 1. The polishing apparatus is
typically partitioned into a polishing section and a cleaning
section. A wafer is firstly transported into the polishing section,
where the wafer is placed in sliding contact with a polishing pad
on a polishing table, while a polishing liquid (slurry) is supplied
onto the polishing pad. The wafer is polished in the presence of
the polishing liquid (step 1). The polished wafer is then
transported to the cleaning section, where the wafer is cleaned
(step 2) and further the cleaned wafer is dried (step 3).
[0008] The wafer that has been processed in this manner is then
transported to a film thickness measuring device provided exterior
of the polishing apparatus (step 4), and a film thickness of the
polished wafer is measured by the film thickness measuring device
(step 5). The film thickness of the wafer is compared with a
predetermined target film thickness (step 6), and if the film
thickness of the wafer has not reached the target film thickness,
then the wafer is transported into the polishing apparatus again,
where the wafer is re-polished, cleaned, and dried. Such
re-polishing (which is so-called rework) is effective at realizing
an accurate film thickness, but on the other hand it takes a
certain time from the first polishing step to the re-polishing
step, lowering the productivity (throughput).
[0009] According the above described polishing method, it is
possible to adjust polishing conditions (such as a polishing time
and a polishing pressure) for subsequent wafers based on the film
thickness measurement result in the external film thickness
measuring device. However, when the adjusted polishing conditions
are applied to the wafer polishing process, several wafers have
already been polished. This means that the adjusted polishing
conditions are not reflected in polishing of those wafers. In order
to reflect the adjusted polishing conditions in polishing of the
next wafer, it is necessary to keep the next wafer waiting until
the film thickness measurement of a preceding wafer is terminated
and the adjustment of the polishing conditions is completed.
However, such an operation results in a lowered productivity
(throughput).
SUMMARY OF THE INVENTION
[0010] The present invention has been made in view of the above
circumstances. It is therefore an object of the present invention
to provide a polishing method capable of reducing a time required
for re-polishing of a substrate, such as a wafer, or eliminating
re-polishing of the substrate itself, and capable of applying
adjusted polishing conditions to polishing of the next substrate
immediately.
[0011] In a first embodiment, a method of polishing a substrate
having a film is provided. The method comprises: performing
polishing of the substrate in a polishing section; transporting the
polished substrate to a wet-type film thickness measuring device
prior to cleaning and drying of the substrate; measuring a
thickness of the film by the wet-type film thickness measuring
device; comparing the thickness with a predetermined target value;
and if the thickness has not reached the predetermined target
value, performing re-polishing of the substrate in the polishing
section prior to cleaning and drying of the substrate.
[0012] In a second embodiment, a method of polishing a substrate
having a film is provided. The method comprises: polishing the
substrate while measuring a thickness of the film with a film
thickness sensor; terminating polishing of the substrate when a
measured value of the thickness of the film, obtained from the film
thickness sensor, reaches a predetermined value; transporting the
polished substrate to a wet-type film thickness measuring device;
measuring a thickness of the film by the wet-type film thickness
measuring device; calibrating the film thickness sensor based on
the measured value of the thickness of the film obtained from the
film thickness sensor and a measured value of the thickness of the
film obtained from the wet-type film thickness measuring device;
polishing a subsequent substrate while measuring a thickness of a
film of the subsequent substrate with the calibrated film thickness
sensor; and terminating polishing of the subsequent substrate when
the thickness of the film reaches a predetermined target value.
[0013] In a third embodiment, a method of polishing a substrate
having a film is provided. The method comprises: performing
polishing of the substrate in a polishing section; transporting the
polished substrate, with its surface wet, to a wet-type film
thickness measuring device; measuring a thickness of the film by
the wet-type film thickness measuring device; comparing the
thickness with a predetermined target value; and if the thickness
has not reached the predetermined target value, performing
re-polishing of the substrate in the polishing section prior to
cleaning and drying of the substrate.
[0014] FIG. 2 is a flowchart showing a polishing method according
to the first embodiment and the third embodiment described above.
As shown in FIG. 2, before a polished substrate (e.g., wafer) is
cleaned and dried, a film thickness of the wafer in a wet state is
measured. If the measured film thickness has not reached the target
value, then the substrate is returned to the polishing section,
where the substrate is re-polished. Since the substrate is
re-polished prior to cleaning and drying of the substrate, a time
required for re-polishing the substrate can be shortened. As a
result, a throughput can be improved. Moreover, polishing
conditions (e.g., polishing time and polishing pressure) adjusted
based on the film-thickness measurement result can be readily
applied to polishing of the next substrate. Therefore, the
throughput can be improved.
[0015] According to the above-described second embodiment, the film
thickness sensor is calibrated using the measured values of the
film thickness obtained by the wet-type film thickness measuring
device which can achieve highly accurate measurement. Therefore, an
accuracy of in-situ film thickness measurement that is performed
during polishing of subsequent substrates can be improved. As a
result, re-polishing of the substrate can be eliminated. Moreover,
the polishing conditions (e.g., polishing time and polishing
pressure) adjusted based on the film-thickness measurement result
can be applied to polishing of the next substrate. Therefore, the
throughput can be improved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a flowchart illustrating a conventional wafer
polishing method;
[0017] FIG. 2 is a flowchart illustrating an embodiment of a
polishing method;
[0018] FIG. 3 is a view showing a polishing apparatus which can
perform the embodiment of the polishing method;
[0019] FIG. 4 is a perspective view schematically showing a first
polishing unit;
[0020] FIG. 5 is a cross-sectional view of a top ring shown in FIG.
4;
[0021] FIGS. 6A and 6B are schematic views of a wet-type film
thickness measuring device;
[0022] FIG. 7 is a view showing an example of a cross-sectional
structure of a wafer;
[0023] FIGS. 8A and 8B are diagrams showing the polishing method
for the wafer shown in FIG. 7;
[0024] FIG. 9 is a flowchart for illustrating the polishing method
shown in FIG. 8A and FIG. 8B;
[0025] FIGS. 10A, 10B, 10C, and 10D are diagrams showing another
example of the polishing method for the wafer shown in FIG. 7;
[0026] FIG. 11 is a flowchart for illustrating the polishing method
shown in FIG. 10A through FIG. 10D;
[0027] FIGS. 12A, 12B, 12C, and 12D are diagrams showing still
another example of the polishing method for the wafer shown in FIG.
7;
[0028] FIG. 13 is a flowchart for illustrating the polishing method
shown in FIG. 12A through FIG. 12D;
[0029] FIG. 14 is a cross-sectional view of a multilayer structure
constituted by a tungsten film, a barrier film, and a dielectric
film;
[0030] FIGS. 15A and 15B are diagrams showing the polishing method
for the wafer shown in FIG. 14;
[0031] FIG. 16 is a flowchart for illustrating the polishing method
shown in FIG. 15A and FIG. 15B;
[0032] FIG. 17 is a cross-sectional view showing a wafer having an
interlayer dielectric film (ILD);
[0033] FIGS. 18A and 18B are diagrams showing an example of the
polishing method for the wafer shown in FIG. 17;
[0034] FIG. 19 is a flowchart for illustrating the polishing method
shown in FIG. 18A and FIG. 18B;
[0035] FIG. 20 is a cross-sectional view of a wafer showing a STI
(shallow trench isolation) process;
[0036] FIGS. 21A and 21B are diagrams showing the polishing method
for the wafer shown in FIG. 20;
[0037] FIG. 22 is a flowchart for illustrating the polishing method
shown in FIG. 21A and FIG. 21B;
[0038] FIG. 23 is a cross-sectional view of a wafer having a
multilayer structure to which CMP is applied in a process of
forming high-k metal gate;
[0039] FIGS. 24A, 24B, 24C, and 24D are diagrams showing an example
of the polishing method for the wafer shown in FIG. 23;
[0040] FIG. 25 is a flowchart for illustrating the polishing method
shown in FIG. 24A through FIG. 24D;
[0041] FIG. 26 is a flowchart for illustrating another example of
the polishing method shown in FIG. 24A through FIG. 24D;
[0042] FIG. 27 is a schematic cross-sectional view showing a first
polishing unit having an eddy current film thickness sensor and an
optical film thickness sensor;
[0043] FIG. 28 is a schematic view illustrating a principle of the
optical film thickness sensor;
[0044] FIG. 29 is a plan view showing a positional relationship
between the wafer and a polishing table;
[0045] FIG. 30 is a diagram showing a spectrum created by an
operation controller;
[0046] FIG. 31 is a diagram illustrating a process of determining a
current film thickness from a comparison of the created spectrum
with a plurality of reference spectra;
[0047] FIG. 32 is a schematic view showing two spectra
corresponding to a film thickness difference .DELTA..alpha.;
[0048] FIG. 33 is a diagram illustrating a principle of an eddy
current film thickness sensor;
[0049] FIG. 34 is a diagram showing a graph drawn by plotting
coordinates X and Y, which change with a film thickness, on a XY
coordinate system;
[0050] FIG. 35 shows a graph obtained by rotating the graph in FIG.
34 through 90 degrees in a counterclockwise direction and further
translating the resulting graph;
[0051] FIG. 36 is a graph showing arcuate paths of the coordinates
X and Y that change in accordance with a distance between a coil
and a wafer;
[0052] FIG. 37 is a graph showing an angle .theta. that varies in
accordance with polishing time; and
[0053] FIG. 38 is a schematic view showing details of an optical
film thickness measuring head of a wet-type film thickness
measuring device.
DETAILED DESCRIPTION
[0054] Embodiments will be described with reference to the
drawings.
[0055] FIG. 3 is a view showing a polishing apparatus capable of
performing an embodiment of a polishing method. As shown in FIG. 3,
the polishing apparatus has a housing 1 in a rectangular shape. An
interior space of the housing 1 is divided by partitions 1a and 1b
into a load-unload section 2, a polishing section 3, and a cleaning
section 4. The polishing apparatus includes an operation controller
5 configured to control wafer processing operations.
[0056] The load-unload section 2 has front load sections 20 on
which wafer cassettes are placed, respectively. A plurality of
wafers (substrates) are stored in each wafer cassette. The
load-unload section 2 has a moving mechanism 21 extending along an
arrangement direction of the front load sections 20. Two transfer
robots (loaders) 22 are provided on the moving mechanism 21, so
that the transfer robots 22 can move along the arrangement
direction of the front load sections 20. Each transfer robot 22 is
able to access the wafer cassettes mounted to the front load
sections 20.
[0057] The polishing section 3 is an area where a wafer (i.e., a
substrate) is polished. This polishing section 3 includes a first
polishing unit 3A, a second polishing unit 3B, a third polishing
unit 3C, and a fourth polishing unit 3D. As shown in FIG. 3, the
first polishing unit 3A includes a first polishing table 30A
supporting a polishing pad 10 having a polishing surface, a first
top ring 31A for holding a wafer and pressing the wafer against the
polishing pad 10 on the polishing table 30A so as to polish the
wafer, a first polishing liquid supply mechanism 32A for supplying
a polishing liquid (e.g., slurry) and a dressing liquid (e.g., pure
water) onto the polishing pad 10, a first dresser 33A for dressing
the polishing surface of the polishing pad 10, and a first atomizer
34A for ejecting a liquid (e.g., pure water) or a mixture of a
liquid (e.g., pure water) and a gas (e.g., nitrogen gas) in an
atomized state onto the polishing surface of the polishing pad
10.
[0058] Similarly, the second polishing unit 3B includes a second
polishing table 30B supporting a polishing pad 10, a second top
ring 31B, a second polishing liquid supply mechanism 32B, a second
dresser 33B, and a second atomizer 34B. The third polishing unit 3C
includes a third polishing table 30C supporting a polishing pad 10,
a third top ring 31C, a third polishing liquid supply mechanism
32C, a third dresser 33C, and a third atomizer 34C. The fourth
polishing unit 3D includes a fourth polishing table 30D supporting
a polishing pad 10, a fourth top ring 31D, a fourth polishing
liquid supply mechanism 32D, a fourth dresser 33D, and a fourth
atomizer 34D.
[0059] The first polishing unit 3A, the second polishing unit 3B,
the third polishing unit 3C, and the fourth polishing unit 3D have
the same configuration. Therefore, the first polishing unit 3A will
be described below with reference to FIG. 4. FIG. 4 is a
perspective view schematically showing the first polishing unit 3A.
In FIG. 4, the dresser 33A and the atomizer 34A are omitted.
[0060] The polishing table 30A is coupled to a table motor 19
through a table shaft 30a, so that the polishing table 30A is
rotated by the table motor 19 in a direction indicated by arrow.
The table motor 19 is located below the polishing table 30A. The
polishing pad 10 is attached to an upper surface of the polishing
table 30A. The polishing pad 10 has an upper surface 10a, which
provides a polishing surface for polishing the wafer W. The top
ring 31A is secured to a lower end of the top ring shaft 16. The
top ring 31A is configured to hold the wafer W on its lower surface
by vacuum suction. The top ring shaft 16 is elevated and lowered by
an elevating mechanism (not shown in the drawing).
[0061] An optical film thickness sensor 40 and an eddy current film
thickness sensor 60 each for obtaining film thickness signal that
varies in accordance with a film thickness of the wafer W are
arranged in the polishing table 30A. These film thickness sensors
40 and 60 are rotated in unison with the polishing table 30A as
illustrated by arrow A and obtain the film thickness signals of the
wafer W held by the top ring 31A. The optical film thickness sensor
40 and the eddy current film thickness sensor 60 are coupled to the
operation controller 5 shown in FIG. 3 so that the film thickness
signals obtained by these film thickness sensors 40 and 60 are
transmitted to the operation controller 5. The operation controller
5 is configured to produce from the film thickness signal a film
thickness index value that directly or indirectly indicates the
film thickness.
[0062] Further, a torque current measuring device 70 is provided
for measuring an input current (i.e., a torque current) of the
table motor 19 that rotates the polishing table 30A. A torque
current value measured by the torque current measuring device 70 is
sent to the operation controller 5, which monitors the torque
current value during polishing of the wafer W.
[0063] The wafer W is polished as follows. The top ring 31A and the
polishing table 30A are rotated in directions as indicated by
arrows, while the polishing liquid (i.e., the slurry) is supplied
onto the polishing pad 10 from the polishing liquid supply
mechanism 32A. In this state, the top ring 31A, holding the wafer W
on its lower surface, is lowered by the top ring shaft 16 and
presses the wafer W against the polishing surface 10a of the
polishing pad 10. The surface of the wafer W is polished by a
mechanical action of abrasive grains contained in the polishing
liquid and a chemical action of the polishing liquid. After
polishing of the wafer W, dressing (or conditioning) of the
polishing surface 10a is performed by the dresser 33A. Further,
high-pressure fluid is supplied from the atomizer 34A onto the
polishing surface 10a to remove polishing debris and the abrasive
grains from the polishing surface 10a.
[0064] The top ring 31A is configured to be capable of pressing a
plurality of zones of the wafer separately against the polishing
pad 10. FIG. 5 is a cross-sectional view of the top ring 31A shown
in FIG. 4. The top ring 31A has a top ring body 57 coupled to the
top ring shaft 16 via a universal joint 56, and a retaining ring 58
provided on a lower portion of the top ring body 57.
[0065] The top ring 31A further has a flexible membrane 62 to be
brought into contact with the wafer W, and a chucking plate 63 that
holds the membrane 62. The membrane 62 and the chucking plate 63
are disposed below the top ring body 57. Four pressure chambers
(air bags) P1, P2, P3, and P4 are provided between the membrane 62
and the chucking plate 63. The pressure chambers P1, P2, P3, and P4
are formed by the membrane 62 and the chucking plate 63. The
central pressure chamber P1 has a circular shape, and the other
pressure chambers P2, P3, and P4 have an annular shape. These
pressure chambers P1, P2, P3, and P4 are in a concentric
arrangement.
[0066] Pressurized fluid (e.g., pressurized air) is supplied into
the pressure chambers P1, P2, P3, and P4 or vacuum is developed in
the pressure chambers P1, P2, P3, and P4 by a pressure regulator 64
through fluid passages F1, F2, F3, and F4, respectively. The
pressures in the pressure chambers P1, P2, P3, and P4 can be
changed independently to thereby independently adjust loads on four
zones of the wafer W: a central portion; an inner intermediate
portion; an outer intermediate portion; and a peripheral portion.
Further, by elevating or lowering the top ring 31A in its entirety,
the retaining ring 58 can press the polishing pad 10 at a
predetermined load.
[0067] A pressure chamber P5 is formed between the chucking plate
63 and the top ring body 57. Pressurized fluid is supplied into the
pressure chamber P5 or vacuum is developed in the pressure chamber
P5 by the pressure regulator 64 through a fluid passage F5. With
these operations, the chucking plate 63 and the membrane 62 in
their entirety can move up and down. The retaining ring 58 is
arranged around the wafer W so as to prevent the wafer W from
coming off the top ring 31A during polishing. The membrane 62 has
an opening in a portion that forms the pressure chamber P3, so that
the wafer W can be held by the top ring 31A via the vacuum suction
by producing vacuum in the pressure chamber P3. Further, the wafer
W can be released from the top ring 31A by supplying nitrogen gas
or clean air into the pressure chamber P3.
[0068] The operation controller 5 is configured to determine target
values of internal pressure of the pressure chambers P1, P2, P3,
and P4 based on the film thickness index values in the zones on the
wafer surface corresponding to the pressure chambers P1, P2, P3,
and P4. The operation controller 5 sends command signals of the
target values of internal pressure to the pressure regulator 64 so
as to control the pressure regulator 64 such that the internal
pressures of the pressure chambers P1, P2, P3, and P4 accord with
the target values. In this manner, the top ring 31A having the
multiple pressure chambers can press the respective zones on the
wafer surface separately in accordance with the polishing progress,
and can therefore polish the film uniformly.
[0069] Referring back to FIG. 3, a first linear transporter 6 is
arranged adjacent to the first polishing unit 3A and the second
polishing unit 3B. This first linear transporter 6 is configured to
transport the wafer between four transfer positions (i.e., a first
transfer position TP1, a second transfer position TP2, a third
transfer position TP3, and a fourth transfer position TP4). A
second linear transporter 7 is arranged adjacent to the third
polishing unit 3C and the fourth polishing unit 3D. This second
linear transporter 7 is configured to transport the wafer between
three transfer positions (i.e., a fifth transfer position TP5, a
sixth transfer position TP6, and a seventh transfer position
TP7).
[0070] The wafer is transported to the first polishing unit 3A and
the second polishing unit 3B by the first linear transporter 6. The
top ring 31A of the first polishing unit 3A is moved between a
position above the polishing table 30A and the second transfer
position TP2 by the swinging motion of the top ring 31A. Therefore,
the wafer is transferred to and from the top ring 31A at the second
transfer position TP2. Similarly, the top ring 31B of the second
polishing unit 3B is moved between a position above the polishing
table 30B and the third transfer position TP3, and the wafer is
transferred to and from the top ring 31B at the third transfer
position TP3. The top ring 31C of the third polishing unit 3C is
moved between a position above the polishing table 30C and the
sixth transfer position TP6, and the wafer is transferred to and
from the top ring 31C at the sixth transfer position TP6. The top
ring 31D of the fourth polishing unit 3D is moved between a
position above the polishing table 30D and the seventh transfer
position TP7, and the wafer is transferred to and from the top ring
31D at the seventh transfer position TP7.
[0071] A lifter 11 for receiving the wafer from the transfer robot
22 is provided adjacent to the first transfer position TP1. The
wafer is transported from the transfer robot 22 to the first linear
transporter 6 via the lifter 11. A shutter (not shown in the
drawing) is provided on the partition 1a at a position between the
lifter 11 and the transfer robot 22. When the wafer is to be
transported, this shutter is opened to allow the transfer robot 22
to deliver the wafer to the lifter 11.
[0072] A swing transporter 12 is provided between the first linear
transporter 6, the second linear transporter 7, and the cleaning
section 4. Transporting of the wafer from the first linear
transporter 6 to the second linear transporter 7 is performed by
the swing transporter 12. The wafer is transported to the third
polishing unit 3C and/or the fourth polishing unit 3D by the second
linear transporter 7.
[0073] A wet-type film thickness measuring device 80 is provided
between the polishing section 3 and the cleaning section 4. More
specifically, the wet-type film thickness measuring device 80 is
located adjacent to the fourth polishing unit 3D of the polishing
section 3. A transfer robot 79 is provided between the second
linear transporter 7 and the wet-type film thickness measuring
device 80. The wafer that has been polished in the polishing
section 3 is transported from the second linear transporter 7 to
the wet-type film thickness measuring device 80 by the transfer
robot 79. Therefore, the wafer is transported between the polishing
section 3 and the wet-type film thickness measuring device 80 by a
transporting device which is constituted by the second linear
transporter 7 and the transfer robot 79. The transfer robot 79 may
be omitted so that the wafer is transported to the wet-type film
thickness measuring device 80 directly by the second linear
transporter 7. In this case, the wafer is transported between the
polishing section 3 and the wet-type film thickness measuring
device 80 by a transporting device which is constituted by the
second linear transporter 7.
[0074] The wet-type film thickness measuring device 80 is a
wet-type optical film thickness measuring device capable of
measuring a film thickness of a wet wafer prior to a drying
process. This wet-type film thickness measuring device 80 is
configured to measure a thickness of an optically transparent film
formed on the wafer with a liquid (typically pure water) existing
between the wafer and an optical film thickness measuring head. The
liquid, whose physical property is known, is present with a
predetermined thickness between the wafer and the film thickness
measuring head. The wet-type film thickness measuring device 80
will be described with reference to FIG. 6A and FIG. 6B each
showing a schematic view of the wet-type film thickness measuring
device 80. The wet-type film thickness measuring device 80 includes
a water reservoir 81 in which pure water is stored, a holding
device 82 configured to hold the wafer W via vacuum suction, and an
optical film thickness measuring head 84 configured to measure the
film thickness of the wafer W.
[0075] The wafer W is placed onto support arms 83 by the
above-described transfer robot 79. The wafer W on the support arms
83 is held by the holding device 82, and then the support arms 83
move in a direction away from the wafer W. The holding device 82 is
configured to rotate the wafer W about its center and is further
configured to move the wafer W in a vertical direction. An
orientation detector 85 for detecting an orientation of the wafer W
in a circumferential direction thereof is provided above the water
reservoir 81. This orientation detector 85 is configured to detect
the orientation of the wafer W by detecting a cutout portion, which
is called a notch or an orientation flat, formed on a periphery of
the wafer W. While the wafer W is rotated by the holding device 82,
the orientation detector 85 detects the orientation of the wafer W.
The wafer W is further rotated by the holding device 82 until the
wafer W is oriented to a predetermined direction.
[0076] With the wafer W oriented to the predetermined direction,
the holding device 82 is lowered to immerse the wafer W into the
water in the water reservoir 81. A plurality of measurement
pedestals 87 are disposed in the water reservoir 81, so that the
wafer W is placed onto these measurement pedestals 87, as shown in
FIG. 6B. When the periphery of the wafer W is placed on the
measurement pedestals 87, the wafer W is maintained in a horizontal
position. The water reservoir 81 has its bottom constituted by a
transparent window 90. The optical film thickness measuring head 84
is arranged below the transparent window 90. The optical film
thickness measuring head 84 is configured to irradiate the wafer W
in the water with light through the transparent window 90, receive
the light reflected from the wafer W, and determine the film
thickness of the wafer W from optical information contained in the
reflected light. The principle of the film thickness measurement of
the optical film thickness measuring head 84 is basically the same
as that of the optical film thickness sensor 40. A known film
thickness measuring device as disclosed in Japanese laid-open
patent publication No. 9-109023 may be used as the wet-type film
thickness measuring device 80.
[0077] The optical film thickness measuring head 84 is coupled to a
horizontally moving mechanism 92, which is configured to move the
optical film thickness measuring head 84 horizontally during
measurement of the film thickness. The measurement pedestals 87
have a wafer rotating mechanism (now shown) for rotating the wafer
W, so that the measurement pedestals 87 can adjust the orientation
of the wafer W (i.e., the position of the wafer W in the
circumferential direction) that has been detected by the
orientation detector 85. The horizontally moving mechanism 92
enables the optical film thickness measuring head 84 to measure the
film thickness at multiple measurement points along a radial
direction of the wafer W. Further, the combination of the
measurement pedestals 87 and the horizontally moving mechanism 92
enables the optical film thickness measuring head 84 to measure the
film thickness at a desired point on the wafer W. During
measurement of the film thickness, the wafer W in the water
reservoir 81 is in a stationary state and placed horizontally.
Therefore, the wet-type film thickness measuring device 80 can
measure the film thickness more accurately than the optical film
thickness measuring sensor 40 that measures the film thickness of
the rotating wafer. The measured value of the film thickness
obtained by the wet-type film thickness measuring device 80 is
transmitted to the operation controller 5.
[0078] Referring back to FIG. 3, a temporary base 72 for the wafer
W is arranged beside the swing transporter 12. This temporary base
72 is mounted to a non-illustrated frame. As shown in FIG. 3, the
temporary base 72 is arranged adjacent to the first linear
transporter 6 and located between the first linear transporter 6
and the cleaning section 4. The swing transporter 12 is configured
to move between the fourth transfer position TP4, the fifth
transfer position TP5, and the temporary base 72. In this
embodiment, when the wafer is transported between the polishing
units 3A to 3D, the wafer is released from the top ring and is
delivered to other polishing unit through the linear transporters 6
and 7. It is noted that a device for transporting the wafer between
the polishing units is not limited to this embodiment. For example,
the top ring may transport the wafer directly to other polishing
unit while holding the wafer thereon.
[0079] The wafer W, placed on the temporary base 72, is transported
to the cleaning section 4 by a first transfer robot 77 of the
cleaning section 4. As shown in FIG. 3, the cleaning section 4
includes a first cleaning device 73 and a second cleaning device 74
for cleaning the polished wafer with a cleaning liquid, and a
drying device 75 for drying the cleaned wafer. The first transfer
robot 77 is configured to transport the wafer from the temporary
base 72 to the first cleaning device 73 and further transport the
wafer from the first cleaning device 73 to the second cleaning
device 74. A second transfer robot 78 is arranged between the
second cleaning device 74 and the drying device 75. This second
transfer robot 78 is operable to transport the wafer from the
second cleaning device 74 to the drying device 75.
[0080] The dried wafer is removed from the drying device 75 by the
transfer robot 22 and returned to the wafer cassette. In this
manner, a sequence of processes including polishing, film-thickness
measuring, cleaning, and drying is performed on the wafer.
[0081] Next, a method of polishing a wafer using the
above-described polishing apparatus will be described. FIG. 7 is a
view showing an example of a cross-sectional structure of a wafer
to be polished. In this wafer, a first hard mask film 102, which is
an oxide film of SiO.sub.2 or the like, is formed on an interlayer
dielectric film 101 which is made of SiO.sub.2 or a low-k material.
A second hard mask film 104 made of a metal is formed on the first
hard mask film 102. A barrier film 105 made of a metal is formed so
as to cover the second hard mask film 104 and a trench formed in
the interlayer dielectric film 101. The interlayer dielectric film
101 and the first hard mask film 102 constitute a dielectric film
103, while the second hard mask film 104 and the barrier film 105
constitute a conductive film 106. Although not shown, in another
example of the multilayer structure, the first hard mask film 102
and the second hard mask film 104 may not be provided. In this
case, the barrier film 105 constitutes the conductive film 106, and
the interlayer dielectric film 101 constitutes the dielectric film
103.
[0082] After the barrier film 105 is formed, the wafer is plated
with copper, so that the trench is filled with copper and a copper
film 107 as a metal film is deposited on the barrier film 105.
Thereafter, polishing of the wafer is performed by the polishing
apparatus to remove unnecessary films, i.e., the copper film 107,
the barrier film 105, the second hard mask film 104, and the first
hard mask film 102, leaving copper in the trench. This copper
remaining in the trench, which is a part of the copper film 107,
forms interconnects 108 of a semiconductor device. The polishing
process is terminated when a thickness of the dielectric film 103
reaches a predetermined value, i.e., when a height of the
interconnects 108 reaches a predetermined value, as indicated by a
dotted line in FIG. 7.
[0083] FIGS. 8A and 8B are diagrams showing a polishing method for
the wafer shown in FIG. 7. The wafer having the above multilayer
structure is polished in two steps by the first polishing unit 3A
and the second polishing unit 3B, and at the same time, another
wafer of the same structure is polished in two steps by the third
polishing unit 3C and the fourth polishing unit 3D. The first step
of the two-step polishing process is a process of removing the
unnecessary copper film 107 until the barrier film 105 is exposed,
as shown in FIG. 8A. The second step is a process of removing the
barrier film 105, the second hard mask film 104, and the first hard
mask film 102, and then polishing the interlayer dielectric film
101 until the thickness of the dielectric film 103 reaches a
predetermined value, i.e., until the height of the interconnects
108 in the trench reaches a predetermined target value, as shown in
FIG. 8B. The first step of the two-step polishing process is
carried out in the first polishing unit 3A and the third polishing
unit 3C, and the second step is carried out in the second polishing
unit 3B and the fourth polishing unit 3D. In this manner, the two
wafers are concurrently polished by the polishing units 3A and 3B
and the polishing units 3C and 3D, respectively.
[0084] In polishing of the dielectric film 103, a film thickness
signal of the dielectric film 103 is obtained by the optical film
thickness sensor 40. The operation controller 5 produces from the
film thickness signal a film thickness index value which directly
or indirectly indicates the thickness of the dielectric film 103
and stops polishing of the dielectric film 103 when the film
thickness index value reaches a predetermined threshold value (i.e.
when the thickness of the dielectric film 103 reaches a
predetermined target value). Alternatively, the operation
controller 5 may determine a polishing end point of the dielectric
film 103 from a removal amount of the dielectric film 103 (i.e., an
amount of the dielectric film 103 removed by the polishing
process). Specifically, instead of producing the film thickness
index value, the operation controller 5 may produce from the film
thickness signal a removal index value which directly or indirectly
indicates the removal amount of the dielectric film 103, and may
stop polishing of the dielectric film 103 when the removal index
value reaches a threshold value (i.e., when the removal amount of
the dielectric film 103 reaches a predetermined target value). In
this case also, it is possible to polish the dielectric film 103
until the thickness thereof reaches the predetermined target
value.
[0085] FIG. 9 is a flowchart for illustrating a method of polishing
the wafer shown in FIGS. 8A and 8B. In step 1, while the polishing
liquid is supplied onto the polishing pad 10 on the first polishing
table 30A or the third polishing table 30C, the copper film (i.e.,
a metal film) 107 is polished until the barrier film 105,
constituting the conductive film 106, is exposed. This step 1
corresponds to the first polishing process shown in FIG. 8A. In
step 2, while the polishing liquid is supplied onto the polishing
pad 10 on the second polishing table 30B or the fourth polishing
table 30D, the conductive film 106 is polished until the dielectric
film 103 is exposed, and further the dielectric film 103 is
polished until its thickness reaches a predetermined target value.
More specifically, the barrier film 105, the second hard mask film
104, and the first hard mask film 102 are removed, and further the
interlayer dielectric film 101 is polished. This step 2 corresponds
to the second polishing process shown in FIG. 8B.
[0086] In step 3, the wafer is water-polished while pure water,
instead of the polishing liquid, is supplied onto the polishing pad
10 on the second polishing table 30B or the fourth polishing table
30D. This water polishing removes the polishing liquid and
polishing debris from the wafer. In step 4, the polished wafer,
with its surface wet, is transported to the wet-type film thickness
measuring device 80.
[0087] In step 5, the thickness of the polished dielectric film 103
is measured by the wet-type film thickness measuring device 80.
Measurement result of the film thickness is sent to the operation
controller 5. In step 6, the operation controller 5 compares the
measured current film thickness with the predetermined target
value. If the measured film thickness has not reached the target
value, then the operation controller 5 calculates an additional
polishing time that is necessary to achieve the target value from a
difference between the measured film thickness and the target value
(step 7). The additional polishing time can be calculated from a
polishing rate and the difference between the current film
thickness and the target value of the dielectric film 103. The
wafer is again transported to the polishing pad 10 on the second
polishing table 30B or the fourth polishing table 30D, and is
re-polished for the calculated additional polishing time while the
polishing liquid is supplied onto the polishing pad 10. If the
measured film thickness has reached the target value, then the
wafer is transported to the cleaning section 4, where the wafer is
cleaned and dried (step 8). The film thickness measurement in the
steps 4 and 5 and the comparison of the measured film thickness
with the target value in the step 6 after re-polishing of the wafer
may be omitted.
[0088] Measurement of the film thickness in the wet-type film
thickness measuring device 80 and/or re-polishing of the wafer may
cause subsequent wafer(s) to wait for processing thereof in the
polishing unit or other unit. In such a case, in order to prevent
an increase in defects, such as drying and corrosion, on a surface
of the wafer waiting for processing, pure water or a chemical
liquid having a cleaning effect or a corrosion preventing effect,
may be sprayed intermittently onto the wafer held by the top ring,
or held by the linear transporter at the transfer position, by
means of a spray (not shown) which is installed along a wafer
transport route, e.g., on the first linear transporter 6, the
second linear transporter 7, or the swing transporter 12.
Furthermore, the operation controller 5 may calculate a delay in a
polishing start time of the subsequent wafer(s), due to
re-polishing of the preceding wafer, so as to adjust a polishing
time of the subsequent wafer(s) or a timing of starting polishing
of the subsequent wafer(s). It is also possible to set a process
waiting time of the subsequent wafer(s) in advance for permitting
re-polishing of the preceding wafer, in order to control a timing
of carrying the subsequent wafer(s) into the polishing apparatus.
Such an operation for the subsequent wafer(s), associated with
re-polishing of the preceding wafer, can also be applied to
embodiments which will be discussed later.
[0089] The wet-type film thickness measuring device 80 measures the
film thickness at desired measurement points on the wafer, and the
operation controller 5 creates a polishing profile of the wafer
from the measured values of the film thickness. The polishing
profile represents a cross-sectional shape of the film. The
operation controller 5 is configured to control the polishing
pressure of the top ring 31A, i.e., the pressures in the pressure
chambers P1, P2, P3, and P4 shown in FIG. 5, based on the polishing
profile created. For example, if the thickness of the film is
larger in the edge of the wafer than in the other area, the
pressure in the pressure chamber P4, corresponding to the edge of
the wafer, is increased.
[0090] Polishing conditions, such as the polishing time, the
polishing pressure, the rotational speed of the polishing table,
etc. can be adjusted based on the film thickness measurement
results obtained by the wet-type film thickness measuring device
80. For example, in a case where the end point of each polishing
process is managed by the polishing time, each polishing process is
terminated when a preset polishing time has elapsed. In this case,
based on the film thickness measurement results, the preset
polishing time can be adjusted to an optimal polishing time for
achieving a target film thickness. Furthermore, set pressures (set
polishing pressures) in the pressure chambers P1, P2, P3, and P4
can be adjusted to optimal pressures for making the thickness of
the dielectric film 103 uniform or as desired thickness
distribution. The polishing conditions adjusted in this manner can
be applied to re-polishing of the wafer and can also be applied to
polishing of the subsequent wafer(s). Thus, the subsequent wafer(s)
can be polished for the optimal polishing time with the optimal
polishing pressure. Furthermore, a threshold value of the film
thickness index value or the removal index value for polishing of
the dielectric film 103 can also be adjusted. It is also possible
to additionally polish (over-polish) the wafer for a predetermined
period of time after the film thickness index value or the removal
index value has reached the threshold value. In this case, the
predetermined period of time for over-polishing the wafer may be
adjusted based on the film thickness measurement results.
[0091] The measurement of the film thickness and re-polishing of
the wafer are performed prior to cleaning and drying of the wafer.
This can reduce a time required for starting the re-polishing
process, and therefore can increase the throughput. Further, the
measurement of the film thickness is performed shortly after
polishing of the wafer and the polishing conditions are adjusted
based on the measurement results. Therefore the adjusted polishing
conditions can be applied immediately to polishing of the next
wafer. As a result, it is not necessary to keep the next wafer
waiting for processing thereof, thereby increasing the throughput.
In addition, an accuracy of polishing of the subsequent wafer(s)
can be improved by applying the optimized polishing conditions to
polishing of the subsequent wafer(s).
[0092] Another embodiment of the polishing method will be
described. In this embodiment, the wafer shown in FIG. 7 is
polished using the four polishing tables 30A, 30B, 30C, and 30D.
Specifically, in the first polishing process, the copper film 107
is polished in the first polishing unit 3A until the thickness
thereof reaches a predetermined target value, as shown in FIG. 10A.
In polishing of the copper film 107, the film thickness signal of
the copper film 107 is obtained by the eddy-current film thickness
sensor 60. The operation controller 5 produces from the film
thickness signal the film thickness index value which directly or
indirectly indicates the thickness of the copper film 107, monitors
polishing of the copper film 107 based on the film thickness index
value, and stops polishing of the copper film 107 when the film
thickness index value reaches a predetermined threshold value
(i.e., when the thickness of the copper film 107 reaches the
predetermined target value).
[0093] The wafer that has been polished in the first polishing unit
3A is transported to the second polishing unit 3B, where the wafer
is subjected to the second polishing process. As shown in FIG. 10B,
in the second polishing process, the remaining copper film 107 is
polished until the barrier film 105, lying underneath the copper
film 107, is exposed. A point of time when the barrier film 105 is
exposed as a result of the removal of the copper film 107 is
detected based on the film thickness index value by the operation
controller 5. For example, a removal point of the copper film 107
can be determined from a point when the film thickness index value
reaches a predetermined threshold value. If the polishing liquid
used has properties such that the copper film 107 is polished at a
high polishing rate while the barrier film 105 is polished at a low
polishing rate, polishing of the wafer does not progress any more
once the copper film 107 is removed and the barrier film 105 is
exposed. In this case, the film thickness index value does not
change any more. Therefore, the point of time when the film
thickness index value stops changing may be determined to be the
point of time when the copper film 107 is removed.
[0094] The wafer that has been polished in the second polishing
unit 3B is transported to the third polishing unit 3C, where the
wafer is subjected to the third polishing process. As shown in FIG.
10C, in the third polishing process, the barrier film 105 and the
second hard mask film 104, constituting the conductive film 106,
are removed. Specifically, the conductive film 106 is polished
until the dielectric film 103, lying underneath the conductive film
106, is exposed (i.e., until the first hard mask film 102 is
exposed). In polishing of the conductive film 106, the film
thickness signal of the conductive film 106 is obtained by the
eddy-current film thickness sensor 60. The operation controller 5
produces the film thickness index value of the conductive film 106
from the film thickness signal, monitors polishing of the
conductive film 106 based on the film thickness index value, and
stops polishing of the wafer when the film thickness index value
reaches a predetermined threshold value or when the film thickness
index value stops changing (i.e., when the second hard mask film
104 of the conductive film 106 is removed and the first hard mask
film 102 is exposed).
[0095] The polished wafer is transported from the third polishing
unit 3C to the fourth polishing unit 3D, where the wafer is
subjected to the fourth polishing process. As shown in FIG. 10D, in
the fourth polishing process, the dielectric film 103, which is
constituted by the first hard mask film 102 and the interlayer
dielectric film 101, is polished. Polishing of the dielectric film
103 includes removing of the first hard mask film 102 and polishing
of the interlayer dielectric film 101. The dielectric film 103 is
polished until its thickness reaches a predetermined target
value.
[0096] In polishing of the dielectric film 103, the film thickness
signal of the dielectric film 103 is obtained by the optical film
thickness sensor 40. The operation controller 5 produces the film
thickness index value or the removal index value of the dielectric
film 103 from the film thickness signal and stops polishing of the
dielectric film 103 when the film thickness index value or the
removal index value reaches a predetermined threshold value (i.e.,
when the thickness of the dielectric film 103 or the removal amount
of the film 103 reaches the predetermined target value).
[0097] FIG. 11 is a flowchart for illustrating the wafer polishing
method shown in FIGS. 10A through 10D. In step 1, while the
polishing liquid is supplied onto the polishing pad 10 on the first
polishing table 30A, the copper film (i.e., the metal film) 107 is
polished until its thickness reaches a predetermined target value.
This step 1 corresponds to the first polishing process shown in
FIG. 10A. In step 2, while the polishing liquid is supplied onto
the polishing pad 10 on the second polishing table 30B, the copper
film (i.e., the metal film) 107 is polished until the barrier film
105, constituting the conductive film 106, is exposed. This step 2
corresponds to the second polishing process shown in FIG. 10B.
[0098] In step 3, while the polishing liquid is supplied onto the
polishing pad 10 on the third polishing table 30C, the barrier film
105 and the second hard mask film 104, which constitute the
conductive film 106, are polished. This polishing of the conductive
film 106 is performed until the dielectric film 103 is exposed.
This step 3 corresponds to the third polishing process shown in
FIG. 10C. In step 4, while the polishing liquid is supplied onto
the polishing pad 10 on the fourth polishing table 30D, the
dielectric film 103 is polished until its thickness reaches a
predetermined target value. This step 4 corresponds to the fourth
polishing process shown in FIG. 10D.
[0099] In step 5, the wafer is water-polished while pure water,
instead of the polishing liquid, is supplied onto the polishing pad
10 on the fourth polishing table 30D. The water polishing removes
the polishing liquid and polishing debris from the wafer. In step
6, the polished wafer is transported to the wet-type film thickness
measuring device 80.
[0100] In step 7, the thickness of the polished dielectric film 103
is measured by the wet-type film thickness measuring device 80. The
measurement result of the film thickness is sent to the operation
controller 5. In step 8, the operation controller 5 compares the
measured current film thickness with a predetermined target value.
If the measured film thickness has not reached the predetermined
target value, then the operation controller 5 calculates an
additional polishing time that is necessary to achieve the target
value from a difference between the measured film thickness and the
target value (step 9). The wafer is again transported to the
polishing pad 10 on the fourth polishing table 30D, and is
re-polished for the calculated additional polishing time while the
polishing liquid is supplied onto the polishing pad 10. If the
measured film thickness has reached the target value, the wafer is
then transported to the cleaning section 4, where the wafer is
cleaned and dried (step 10). The film thickness measurement in the
steps 6 and 7 and the comparison of the measured film thickness
with the target value in the step 8 after the re-polishing of the
wafer may be omitted.
[0101] In the third polishing process, it is preferable to use a
highly-selective polishing liquid which contains abrasive grains
and/or chemical composition capable of increasing the polishing
rate of the conductive film 106 while lowering the polishing rate
of the dielectric film 103. When using such a polishing liquid,
polishing of the wafer does not substantially progress after the
dielectric film 103 is exposed. Therefore, the operation controller
5 is able to detect the polishing end point of the conductive film
106 (i.e., the point of time when the dielectric film 103 is
exposed) more accurately.
[0102] When using such a highly-selective polishing liquid in the
third polishing process, it is possible to detect the polishing end
point of the conductive film 106 (i.e., the point of time when the
dielectric film 103 is exposed) based on the torque current of the
table motor 19 (see FIG. 4) that rotates the polishing table 30C. A
frictional force is generated between the wafer and the polishing
pad 10 because the surface of the wafer and the polishing surface
of the polishing pad 10 are placed in sliding contact with each
other during polishing of the wafer. This frictional force varies
depending on the type of film that forms the exposed surface of the
wafer and the type of polishing liquid used.
[0103] The table motor 19 is controlled so as to rotate the
polishing table 30C at a preset constant speed. Accordingly, the
electric current flowing into the table motor 19, i.e., the torque
current, changes upon a change in the frictional force acting
between the wafer and the polishing pad 10. More specifically, when
the frictional force increases, the torque current increases so as
to enable the table motor 19 to exert a higher torque on the
polishing table 30C. Conversely, when the frictional force
decreases, the torque current decreases so that the table motor 19
exerts a lower torque on the polishing table 30C. Thus, the
operation controller 5 can detect the polishing end point of the
conductive film 106 (i.e., the point of time when the dielectric
film 103 is exposed) from the change in the torque current of the
table motor 19. The torque current is measured by the torque
current measuring device 70 shown in FIG. 4.
[0104] Another embodiment of the polishing method will be
described. Also in this embodiment, the wafer shown in FIG. 7 is
polished using the four polishing tables 30A, 30B, 30C, and 30D.
The first polishing process and the second polishing process for
the metal film shown in FIGS. 12A and 12B are performed in the same
manner as in the above-described first polishing process and second
polishing process shown in FIGS. 10A and 10B, and hence duplicate
descriptions thereof will be omitted.
[0105] The wafer that has been polished in the second polishing
unit 3B is transported to the third polishing unit 3C, where the
wafer is subjected to the third polishing process. As shown in FIG.
12C, in the third polishing process, the conductive film 106 is
polished until the dielectric film 103 is exposed, and further the
exposed dielectric film 103 is polished. More specifically, the
barrier film 105 and the second hard mask film 104, which
constitute the conductive film 106, are removed and then the
dielectric film 103, lying underneath the conductive film 106, is
polished until its thickness reaches a predetermined first target
value. The thickness of the dielectric film 103 may be determined
from the amount of the dielectric film 103 removed (which will be
referred to as removal amount). The polishing of the dielectric
film 103 in the third polishing process includes removing of the
first hard mask film 102 and polishing of the interlayer dielectric
film 101, or only polishing of the first hard mask film 102. FIG.
12C illustrates an example in which the first hard mask film 102 is
polished after polishing of the conductive film 106, but the
interlayer dielectric film 101 is not polished.
[0106] In polishing of the conductive film 106 in the third
polishing process, the film thickness signal of the conductive film
106 is obtained by the eddy-current film thickness sensor 60. The
operation controller 5 produces the film thickness index value of
the conductive film 106 from the film thickness signal, monitors
polishing of the conductive film 106 based on the film thickness
index value, and detects a point of time when the film thickness
index value reaches a predetermined threshold value or when the
film thickness index value stops changing (i.e., a point of time
when the conductive film 106 is removed and the dielectric film 103
is exposed). In the third polishing process, the conductive film
106 and the dielectric film 103 are polished successively. In
polishing of the dielectric film 103, the film thickness signal of
the dielectric film 103 is obtained by the optical film thickness
sensor 40. The operation controller 5 produces the film thickness
index value or the removal index value of the dielectric film 103
from the film thickness signal and stops polishing of the
dielectric film 103 when the film thickness index value or the
removal index value reaches a predetermined first threshold value
(i.e., when the thickness or the removal amount of the dielectric
film 103 reaches a predetermined first target value).
[0107] The wafer that has been polished in the third polishing unit
3C is transported to the wet-type film thickness measuring device
80, where the film thickness of the wafer is measured. After the
film thickness measurement, the wafer is transported to the fourth
polishing unit 3D, where the wafer is subjected to the fourth
polishing process. As shown in FIG. 12D, the dielectric film 103 is
polished in the fourth polishing process. The dielectric film 103
is polished until its thickness reaches a predetermined second
target value. The polishing of the dielectric film 103 includes
removing of the first hard mask film 102 and polishing of the
interlayer dielectric film 101, or only polishing of the interlayer
dielectric film 101. FIG. 12D illustrates an example in which the
first hard mask film 102 is removed and subsequently the interlayer
dielectric film 101 is polished.
[0108] FIG. 13 is a flowchart for illustrating the wafer polishing
method shown in FIGS. 12A through 12D. In step 1, while the
polishing liquid is supplied onto the polishing pad 10 on the first
polishing table 30A, the copper film (i.e., the metal film) 107 is
polished until its thickness reaches a predetermined target value.
This step 1 corresponds to the first polishing process shown in
FIG. 12A. In step 2, while the polishing liquid is supplied onto
the polishing pad 10 on the second polishing table 30B, the copper
film (i.e., the metal film) 107 is polished until the barrier film
105, constituting the conductive film 106, is exposed. This step 2
corresponds to the second polishing process shown in FIG. 12B.
[0109] In step 3, while the polishing liquid is supplied onto the
polishing pad 10 on the third polishing table 30C, the barrier film
105 and the second hard mask film 104, which constitute the
conductive film 106, are polished, and further the underlying
dielectric film 103 is polished until its thickness reaches a
predetermined first target value. This step 3 corresponds to the
third polishing process shown in FIG. 12C. In step 4, the wafer is
water-polished while pure water, instead of the polishing liquid,
is supplied onto the polishing pad 10 on the third polishing table
30C. The water polishing removes the polishing liquid and polishing
debris from the wafer. In step 5, the polished wafer is transported
to the wet-type film thickness measuring device 80.
[0110] In step 6, the thickness of the polished dielectric film 103
is measured by the wet-type film thickness measuring device 80. The
measurement result of the film thickness is sent to the operation
controller 5. In step 7, the operation controller 5 compares the
measured current film thickness with a predetermined second target
value which is a final target value of the film thickness. If the
measured film thickness has not reached the second target value,
then the operation controller 5 calculates an additional polishing
time that is necessary to achieve the second target value from a
difference between the measured film thickness and the second
target value (step 8). The additional polishing time can be
calculated from a polishing rate and the difference between the
measured film thickness of the dielectric film 103 and the second
target value. In step 9, the wafer is transported to the polishing
pad 10 on the fourth polishing table 30D, and is re-polished for
the calculated additional polishing time while the polishing liquid
is supplied onto the polishing pad 10. This step 9 corresponds to
the fourth polishing process shown in FIG. 12D. It is also possible
to transport the wafer to the polishing pad 10 on the third
polishing table 30C and to carry out re-polishing of the wafer with
the polishing pad 10 on the third polishing table 30C.
[0111] In step 10, the wafer is water-polished while pure water,
instead of the polishing liquid, is supplied onto the polishing pad
10 on the fourth polishing table 30D. Thereafter, the process flow
returns back to the step 5. If the measured film thickness has
reached the target value, then the wafer is transported to the
cleaning section 4, where the wafer is cleaned and dried (step
11).
[0112] The film thickness of the wafer is expected to reach the
target value by polishing the wafer for the additional polishing
time calculated in the step 8. Therefore, after the steps 9 and 10,
the wafer may be cleaned and dried as the step 11 so that
processing of the wafer is completed, without returning to the step
5 for re-measurement of the film thickness. Such omission of the
measurement of the film thickness after re-polishing of the wafer
can also be applied to the above-described embodiments and to
below-described embodiments.
[0113] The method of this embodiment, which has been described with
reference to FIGS. 12A through 12C and FIG. 13, includes the steps
of polishing a wafer until a film thickness of the wafer reaches a
first target value which is near a second or final target value,
measuring the film thickness of the polished wafer with the
wet-type film thickness measuring device 80, calculating an
additional polishing time that is necessary for eliminating the
difference between the measured current film thickness and the
second target value, and re-polishing the wafer for the additional
polishing time. This embodiment, which includes the steps of
intentionally stopping the polishing of the wafer before the final
target value of the film thickness is reached, measuring the film
thickness, and then re-polishing the wafer, can also be applied to
the above-described embodiments and to below-described
embodiments.
[0114] The above-discussed polishing method can also be applied to
polishing of a wafer having other multilayer structures. FIG. 14 is
a cross-sectional view of a multilayer structure constituted by a
tungsten film, a barrier film, and a dielectric film. In this
wafer, a barrier film 111 as a conductive film is formed so as to
cover a dielectric film 110 and trenches formed in this dielectric
film 110. The dielectric film 110 is formed of SiO.sub.2, a low-k
material, or the like, while the barrier film 111 is formed of a
metal, such as Ti or TiN. A tungsten film 112 as a metal film is
formed so as to cover the barrier film 111. The trenches are filled
with the tungsten film 112. As shown by a dotted line in FIG. 14,
the wafer is polished until unnecessary portions of the tungsten
film 112 and the barrier film 111 are removed and the thickness of
the dielectric film 110 reaches a predetermined value. Tungsten
that exists in the trenches is a part of the tungsten film 112 and
this tungsten forms interconnects 113 of a semiconductor
device.
[0115] FIGS. 15A and 15B are diagrams illustrating an exemplary
polishing method for the wafer shown in FIG. 14. The wafer having
the above-described multilayer structure is polished in two steps
in the first polishing unit 3A and the second polishing unit 3B
while, at the same time, another wafer having the same construction
is polished in two steps in the third polishing unit 3C and the
fourth polishing unit 3D. As shown in FIG. 15A, the first step of
the two-step polishing process is a process of removing the
tungsten film 112 and the barrier film 111 until the dielectric
film 110 is exposed. As shown in FIG. 15B, the second step is a
process of polishing the dielectric film 110 until the thickness of
the dielectric film 110 reaches a predetermined target value (i.e.
until the height of the interconnects 113 in the trenches reaches a
predetermined target value). The first step of the two-step
polishing process is carried out in the first polishing unit 3A and
the third polishing unit 3C, and the second step is carried out in
the second polishing unit 3B and the fourth polishing unit 3D.
[0116] FIG. 16 is a flowchart for illustrating the wafer polishing
method shown in FIGS. 15A and 15B. In step 1, while the polishing
liquid is supplied onto the polishing pad 10 on the first polishing
table 30A or the third polishing table 30C, the tungsten film
(i.e., the metal film) 112 and the barrier film 111 are polished
until the dielectric film 110 is exposed. This step 1 corresponds
to the first polishing process shown in FIG. 15A. In step 2, while
the polishing liquid is supplied onto the polishing pad 10 on the
second polishing table 30B or the fourth polishing table 30D, the
dielectric film 110 is polished until its thickness reaches a
predetermined target value. This step 2 corresponds to the second
polishing process shown in FIG. 15B.
[0117] In polishing of the dielectric film 110, the film thickness
signal of the dielectric film 110 is obtained by the optical film
thickness sensor 40. The operation controller 5 produces the film
thickness index value or the removal index value of the dielectric
film 110 from the film thickness signal and stops polishing of the
dielectric film 110 when the film thickness index value or the
removal index value reaches a predetermined threshold value (i.e.,
when the thickness of the dielectric film 110 or the removal amount
of the dielectric film 110 reaches the predetermined target
value).
[0118] In step 3, the wafer is water-polished while pure water,
instead of the polishing liquid, is supplied onto the polishing pad
10 on the second polishing table 30B or the fourth polishing table
30D. The water polishing removes the polishing liquid and polishing
debris from the wafer. In step 4, the polished wafer is transported
to the wet-type film thickness measuring device 80.
[0119] In step 5, the thickness of the polished dielectric film 110
is measured by the wet-type film thickness measuring device 80. The
measurement result of the film thickness is sent to the operation
controller 5. In step 6, the operation controller 5 compares the
measured current film thickness with the predetermined target
value. If the measured film thickness has not reached the target
value, then the operation controller 5 calculates an additional
polishing time that is necessary to achieve the target value from a
difference between the measured film thickness and the target value
(step 7). The wafer is again transported to the polishing pad 10 on
the second polishing table 30B or the fourth polishing table 30D,
and is re-polished for the calculated additional polishing time
while the polishing liquid is supplied onto the polishing pad 10.
If the measured film thickness has reached the target value, then
the wafer is transported to the cleaning section 4, where the wafer
is cleaned and dried (step 8). The film thickness measurement in
the steps 4 and 5 and the comparison of the measured film thickness
with the target value in the step 6 after the re-polishing of the
wafer may be omitted.
[0120] Next, polishing of a wafer having another multilayer
structure will be described. FIG. 17 is a cross-sectional view of a
wafer having an interlayer dielectric film (ILD) formed thereon.
This wafer has a multilayer structure including a base layer 120,
metal interconnects 121 formed on the base layer 120, and an
interlayer dielectric film 122 formed by CVD so as to cover the
metal interconnects 121.
[0121] FIGS. 18A and 18B are diagrams illustrating an exemplary
polishing method for the wafer shown in FIG. 17. The wafer having
the above-described multilayer structure is polished in two steps
in the first polishing unit 3A and the second polishing unit 3B
while, at the same time, another wafer having the same construction
is polished in two steps in the third polishing unit 3C and the
fourth polishing unit 3D. As shown in FIG. 18A, the first step of
the two-step polishing process is a process of removing stepped
portions (or protruded portions), formed on a surface of the
interlayer dielectric film 122, until its surface is planarized. As
shown in FIG. 18B, the second step is a process of slightly
polishing the interlayer dielectric film 122 to remove scratches
formed on the surface thereof. The first step of the two-step
polishing process is carried out in the first polishing unit 3A and
the third polishing unit 3C, and the second step is carried out in
the second polishing unit 3B and the fourth polishing unit 3D.
[0122] FIG. 19 is a flowchart for illustrating the wafer polishing
method shown in FIGS. 18A and 18B. In step 1, while the polishing
liquid is supplied onto the polishing pad 10 on the first polishing
table 30A or the third polishing table 30C, the interlayer
dielectric film 122 is polished until the stepped portions (or the
protruded portions) on the surface of the interlayer dielectric
film 122 are removed. This step 1 corresponds to the first
polishing process shown in FIG. 18A. In step 2, while the polishing
liquid is supplied onto the polishing pad 10 on the second
polishing table 30B or the fourth polishing table 30D, the
interlayer dielectric film 122 is polished until its thickness
reaches a predetermined target value. This step 2 corresponds to
the second polishing process shown in FIG. 18B.
[0123] In polishing of the interlayer dielectric film 122, the film
thickness signal of the interlayer dielectric film 122 is obtained
by the optical film thickness sensor 40. The operation controller 5
produces the film thickness index value or the removal index value
of the interlayer dielectric film 122 from the film thickness
signal and stops polishing of the interlayer dielectric film 122
when the film thickness index value or the removal index value
reaches a predetermined threshold value (i.e., when the thickness
of the interlayer dielectric film 122 or the removal amount of the
interlayer dielectric film 122 reaches a predetermined target
value).
[0124] In step 3, the wafer is water-polished while pure water,
instead of the polishing liquid, is supplied onto the polishing pad
10 on the second polishing table 30B or the fourth polishing table
30D. This water polishing removes the polishing liquid and
polishing debris from the wafer. In step 4, the polished wafer is
transported to the wet-type film thickness measuring device 80.
[0125] In step 5, the thickness of the polished interlayer
dielectric film 122 is measured by the wet-type film thickness
measuring device 80. The measurement result of the film thickness
is sent to the operation controller 5. In step 6, the operation
controller 5 compares the measured current film thickness with the
predetermined target value. If the measured film thickness has not
reached the target value, then the operation controller 5
calculates an additional polishing time that is necessary to
achieve the target value from a difference between the measured
film thickness and the target value (step 7). The wafer is again
transported to the polishing pad 10 on the second polishing table
30B or the fourth polishing table 30D, and is re-polished for the
calculated additional polishing time while the polishing liquid is
supplied onto the polishing pad 10. If the measured film thickness
has reached the target value, then the wafer is transported to the
cleaning section 4, where the wafer is cleaned and dried (step 8).
The film thickness measurement in the steps 4 and 5 and the
comparison of the measured film thickness with the target value in
the step 6 after the re-polishing of the wafer may be omitted.
[0126] FIG. 20 is a cross-sectional view of a wafer showing an STI
(shallow trench isolation) process. The wafer shown in FIG. 20 has
a multilayer structure constituted by a silicon substrate 130, an
SiO.sub.2 film 131 formed on the silicon substrate 130, a silicon
nitride film 132 made of Si.sub.3N.sub.4 and formed on the
SiO.sub.2 film 131, and an element isolation dielectric film 133
(hereinafter simply referred to as dielectric film 133) made of
SiO.sub.2, formed by high-density plasma CVD or other technique,
and formed on the silicon nitride film 132. STI trenches are formed
in the stack of the silicon substrate 130, the SiO.sub.2 film 131,
and the silicon nitride film 132. The dielectric film 133 is partly
embedded in the STI trenches.
[0127] FIGS. 21A and 21B are diagrams illustrating an exemplary
polishing method for the wafer shown in FIG. 20. The wafer having
the above-described multilayer structure is polished in two steps
in the first polishing unit 3A and the second polishing unit 3B
while, at the same time, another wafer having the same construction
is polished in two steps in the third polishing unit 3C and the
fourth polishing unit 3D. As shown in FIG. 21A, the first step of
the two-step polishing process is a process of removing the
unnecessary portion of the dielectric film 133 to expose the
silicon nitride film 132. As shown in FIG. 21B, the second step
includes a process of polishing the dielectric film 133 and the
silicon nitride film 132 in order to remove scratches formed on the
surfaces of these films and a process of finally adjusting the
thickness of the dielectric film 133. The first step of the
two-step polishing process is carried out in the first polishing
unit 3A and the third polishing unit 3C, and the second step is
carried out in the second polishing unit 3B and the fourth
polishing unit 3D.
[0128] FIG. 22 is a flowchart for illustrating the wafer polishing
method shown in FIGS. 21A and 21B. In step 1, while the polishing
liquid is supplied onto the polishing pad 10 on the first polishing
table 30A or the third polishing table 30C, the dielectric film 133
is polished until the silicon nitride film 132 is exposed. This
step 1 corresponds to the first polishing process shown in FIG.
21A. In step 2, while the polishing liquid is supplied onto the
polishing pad 10 on the second polishing table 30B or the fourth
polishing table 30D, the dielectric film 133 and the silicon
nitride film 132 are polished until the thickness of the dielectric
film 133 reaches a predetermined target value. This step 2
corresponds to the second polishing process shown in FIG. 21B.
[0129] In step 3, the wafer is water-polished while pure water,
instead of the polishing liquid, is supplied onto the polishing pad
10 on the second polishing table 30B or the fourth polishing table
30D. This water polishing removes the polishing liquid and
polishing debris from the wafer. In step 4, the polished wafer is
transported to the wet-type film thickness measuring device 80.
[0130] In step 5, the thickness of the polished dielectric film 133
is measured by the wet-type film thickness measuring device 80. The
measurement result of the film thickness is sent to the operation
controller 5. In step 6, the operation controller 5 compares the
measured current film thickness with the predetermined target
value. If the measured film thickness has not reached the target
value, then the operation controller 5 calculates an additional
polishing time that is necessary to achieve the target value from a
difference between the measured film thickness and the target value
(step 7). The wafer is again transported to the polishing pad 10 on
the second polishing table 30B or the fourth polishing table 30D,
and is re-polished for the calculated additional polishing time
while the polishing liquid is supplied onto the polishing pad 10.
If the measured film thickness has reached the target value, then
the wafer is transported to the cleaning section 4, where the wafer
is cleaned and dried (step 8). The film thickness measurement in
the steps 4 and 5 and the comparison of the measured film thickness
with the target value in the step 6 after the re-polishing of the
wafer may be omitted.
[0131] Polishing of a wafer having still another multilayer
structure will be described. FIG. 23 is a cross-sectional view of a
wafer having a multilayer structure to which CMP is applied in a
process of forming a high-k metal gate. As shown in FIG. 23, the
multilayer structure is constituted by a silicon substrate 140,
polysilicon 141 formed on the silicon substrate 140, a side wall
142 made of silicon nitride (Si.sub.3N.sub.4) and covering the
polysilicon 141, and a dielectric film 144 formed on the side wall
142.
[0132] As shown in FIGS. 24A through 24D, the wafer is polished in
four steps. The first polishing process is a process of polishing
the dielectric film 144 until its thickness reaches a predetermined
first target value as shown in FIG. 24A, the second polishing
process is a process of polishing the dielectric film 144 until the
side wall 142 is exposed and the thickness of the dielectric film
144 reaches a predetermined second target value as shown in FIG.
24B, the third polishing process is a process of polishing the
dielectric film 144 and the side wall 142 until the polysilicon 141
is exposed and the thickness of the dielectric film 144 reaches a
predetermined third target value as shown in FIG. 24C, and the
fourth polishing process is a process of polishing the dielectric
film 144, the polysilicon 141, and the side wall 142 until the
thickness of the dielectric film 144 reaches a predetermined fourth
target value as shown in FIG. 24D.
[0133] The first polishing process is performed in the first
polishing unit 3A, the second polishing process is performed in the
second polishing unit 3B, the third polishing process is performed
in the third polishing unit 3C, and the fourth polishing process is
performed in the fourth polishing unit 3D. During each polishing
process, the film thickness signal of the dielectric film 144 is
obtained by the optical film thickness sensor 40. Instead of the
optical film thickness sensor 40, a set time or the torque current
measuring device 70 may be used to determine the polishing end
point. The operation controller 5 produces the film thickness index
value or the removal index value of the dielectric film 144 from
the film thickness signal and stops polishing of the dielectric
film 144 when the film thickness index value or the removal index
value reaches a predetermined threshold value (i.e., when the
thickness of the dielectric film 144 or the removal amount of the
dielectric film 144 reaches a predetermined target value).
[0134] FIG. 25 is a flowchart for illustrating the wafer polishing
method shown in FIGS. 24A through 24D. In step 1, while the
polishing liquid is supplied onto the polishing pad 10 on the first
polishing table 30A, the dielectric film 144 is polished until its
thickness reaches a predetermined first target value. This step 1
corresponds to the first polishing process shown in FIG. 24A. In
step 2, while the polishing liquid is supplied onto the polishing
pad 10 on the second polishing table 30B, the dielectric film 144
is polished until the side wall 142 is exposed and the thickness of
the dielectric film 144 reaches a predetermined second target
value. This step 2 corresponds to the second polishing process
shown in FIG. 24B.
[0135] In step 3, the wafer is water-polished while pure water,
instead of the polishing liquid, is supplied onto the polishing pad
10 on the second polishing table 30B. This water polishing removes
the polishing liquid and polishing debris from the wafer. In step
4, the polished wafer is transported to the wet-type film thickness
measuring device 80.
[0136] In step 5, the thickness of the polished dielectric film 144
is measured by the wet-type film thickness measuring device 80. The
measurement result of the film thickness is sent to the operation
controller 5. In step 6, the operation controller 5 compares the
measured current film thickness with the predetermined second
target value. If the measured film thickness has not reached the
second target value, then the operation controller 5 calculates an
additional polishing time that is necessary to achieve the second
target value from a difference between the measured film thickness
and the second target value (step 7). The wafer is again
transported to the polishing pad 10 on the first polishing table
30A or the second polishing table 30B, and is re-polished for the
calculated additional polishing time while the polishing liquid is
supplied onto the polishing pad 10. The film thickness measurement
in the steps 4 and 5 and the comparison of the measured film
thickness with the target value in the step 6 after the
re-polishing of the wafer may be omitted. To which either the first
polishing table 30A or the second polishing table 30B the wafer is
to be transported for re-polishing may be determined based on
whether or not the side wall 142 is exposed or on whether or not
the difference between the measured current film thickness of the
dielectric film 144 and the predetermined second target value is
within a predetermined range. If the measured film thickness has
reached the target value, then the wafer is transported to the
polishing pad 10 on the third polishing table 30C.
[0137] In step 8, while the polishing liquid is supplied onto the
polishing pad 10 on the third polishing table 30C, the dielectric
film 144 and the side wall 142 are polished until the thickness of
the dielectric film 144 reaches a predetermined third target value.
This step 8 corresponds to the third polishing process shown in
FIG. 24C. In step 9, while the polishing liquid is supplied onto
the polishing pad 10 on the fourth polishing table 30D, the
dielectric film 144, the polysilicon 141, and the side wall 142 are
polished until the thickness of the dielectric film 144 reaches a
predetermined fourth target value. This step 9 corresponds to the
fourth polishing process shown in FIG. 24D.
[0138] In step 10, the wafer is water-polished while pure water,
instead of the polishing liquid, is supplied onto the polishing pad
10 on the fourth polishing table 30D. This water polishing removes
the polishing liquid and polishing debris from the wafer. In step
11, the polished wafer is transported to the wet-type film
thickness measuring device 80.
[0139] In step 12, the thickness of the polished dielectric film
144 is measured by the wet-type film thickness measuring device 80.
The measurement result of the film thickness is sent to the
operation controller 5. In step 13, the operation controller 5
compares the measured current film thickness with the predetermined
fourth target value. If the measured film thickness has not reached
the fourth target value, then the operation controller 5 calculates
an additional polishing time that is necessary to achieve the
fourth target value from a difference between the measured film
thickness and the fourth target value (step 14). The wafer is again
transported to the polishing pad 10 on the third polishing table
30C or the fourth polishing table 30D, and is re-polished for the
calculated additional polishing time while the polishing liquid is
supplied onto the polishing pad 10. The film thickness measurement
in the steps 11 and 12 and the comparison of the measured film
thickness with the target value in the step 13 after the
re-polishing of the wafer may be omitted. To which either the third
polishing table 30C or the fourth polishing table 30D the wafer is
to be transported for re-polishing may be determined based on
whether or not the polysilicon 141 is exposed or on whether or not
the difference between the measured current film thickness of the
dielectric film 144 and the predetermined fourth target value is
within a predetermined range. If the measured film thickness has
reached the fourth target value, then the wafer is transported to
the cleaning section 4, where the wafer is cleaned and dried (step
15).
[0140] FIG. 26 is a flowchart of another example for carrying out
the wafer polishing method illustrated in FIGS. 24A through 24D. In
step 1, while the polishing liquid is supplied onto the polishing
pad 10 on the first polishing table 30A, the dielectric film 144 is
polished until its thickness reaches a predetermined first target
value. This step 1 corresponds to the first polishing process shown
in FIG. 24A. In step 2, the wafer is water-polished while pure
water, instead of the polishing liquid, is supplied onto the
polishing pad 10 on the first polishing table 30A. In step 3, the
wafer is transported to the wet-type film thickness measuring
device 80, where the thickness of the dielectric film 144 is
measured. In step 4, the operation controller 5 calculates an
additional polishing time that is necessary for the measured
current film thickness to reach a predetermined second target
value.
[0141] In step 5, the wafer is transported to the polishing pad 10
on the second polishing table 30B, and the dielectric film 144 is
polished for the additional polishing time calculated in step 3
while the polishing liquid is supplied onto the polishing pad 10.
This step 5 corresponds to the second polishing process shown in
FIG. 24B. In step 6, the wafer is water-polished while pure water,
instead of the polishing liquid, is supplied onto the polishing pad
10 on the second polishing table 30B.
[0142] In step 7, the wafer is again transported to the wet-type
film thickness measuring device 80, where the thickness of the
dielectric film 144 is measured. The measurement result of the film
thickness is sent to the operation controller 5. In step 8, the
operation controller 5 compares the measured current film thickness
with the predetermined second target value. If the measured film
thickness has not reached the second target value, then the
operation controller 5 calculates an additional polishing time that
is necessary to achieve the second target value from a difference
between the measured film thickness and the second target value
(step 9). The wafer is again transported to the polishing pad 10 on
the second polishing table 30B, and is re-polished for the
calculated additional polishing time while the polishing liquid is
supplied onto the polishing pad 10. If the measured film thickness
has reached the target value, then the wafer is transported to the
polishing pad 10 on the third polishing table 30C. In the
above-described step 5, the film thickness of the wafer is expected
to reach the second target value by polishing the wafer for the
additional polishing time calculated in the step 4. Therefore, the
film thickness measurement in the step 7 and the comparison of the
measured film thickness with the target value in the step 8 may be
omitted.
[0143] In step 10, while the polishing liquid is supplied onto the
polishing pad 10 on the third polishing table 30C, the dielectric
film 144 and the side wall 142 are polished until the thickness of
the dielectric film 144 reaches a predetermined third target value.
This step 10 corresponds to the third polishing process shown in
FIG. 24C. In step 11, the wafer is water-polished while pure water,
instead of the polishing liquid, is supplied onto the polishing pad
10 on the third polishing table 30C. In step 12, the wafer is
transported to the wet-type film thickness measuring device 80,
where the thickness of the dielectric film 144 is measured. In step
13, the operation controller 5 calculates an additional polishing
time that is necessary for the measured current film thickness to
reach a predetermined fourth target value.
[0144] In step 14, the wafer is transported to the polishing pad 10
on the fourth polishing table 30D, and the dielectric film 144, the
side wall 142, and the polysilicon 141 are polished for the
additional polishing time calculated in the step 13 while the
polishing liquid is supplied onto the polishing pad 10 on the
fourth polishing table 30D. This step 14 corresponds to the fourth
polishing process shown in FIG. 24D. In step 15, the wafer is
water-polished while pure water, instead of the polishing liquid,
is supplied onto the polishing pad 10 on the fourth polishing table
30D.
[0145] In step 16, the wafer is transported to the wet-type film
thickness measuring device 80, where the thickness of the
dielectric film 144 is measured. The measurement result of the film
thickness is sent to the operation controller 5. In step 17, the
operation controller 5 compares the measured current film thickness
with the predetermined fourth target value. If the measured film
thickness has not reached the fourth target value, then the
operation controller 5 calculates an additional polishing time that
is necessary to achieve the fourth target value from a difference
between the measured film thickness and the fourth target value
(step 18). The wafer is again transported to the polishing pad 10
on the fourth polishing table 30D, and is re-polished for the
calculated additional polishing time while the polishing liquid is
supplied onto the polishing pad 10. If the measured film thickness
has reached the target value, then the wafer is transported to the
cleaning section 4, where the wafer is cleaned and dried (step 19).
In the above-described step 14, the film thickness of the wafer is
expected to reach the fourth target value by polishing the wafer
for the additional polishing time calculated in the step 13.
Therefore, the film thickness measurement in the step 16 and the
comparison of the measured film thickness with the target value in
the step 17 may be omitted.
[0146] In the above-discussed embodiments, the film thickness
measurement and the re-polishing process are performed prior to
cleaning and drying of the wafer. Therefore, a time required for
starting re-polishing of the wafer can be shortened. As a result, a
throughput can be improved. Moreover, since the film thickness
measurement is performed right after polishing of the wafer, the
polishing conditions (e.g., polishing time and polishing pressure)
adjusted based on the film-thickness measurement result can be
applied to polishing of the next substrate immediately. Therefore,
there is no need to keep the next wafer waiting for being
processed, and hence the throughput can be improved. In addition,
since the optimized polishing conditions can be applied to the
subsequent wafers, a polishing accuracy can be improved.
[0147] In the case where the optical film thickness measuring
sensor 60 is used for detecting the polishing end point, it is
possible to carry out a calibration of the optical film thickness
measuring sensor 60 with use of the measured value of the film
thickness obtained by the wet-type film thickness measuring device
80. After the optical film thickness measuring sensor 60 is
calibrated, the film thickness index value or the removal index
value, both of which are obtained from the film thickness signal of
the optical film thickness measuring sensor 60, has a correlation
with the measured value of the film thickness obtained by the
wet-type film thickness measuring device 80. Therefore, it is
possible to maintain the polishing accuracy even if the film
thickness measurement in the wet-type film thickness measuring
device 80 is omitted.
[0148] Specifically, highly-accurate polishing of the wafer can be
realized by: polishing the wafer while measuring the film thickness
with the optical film thickness measuring sensor 60; terminating
polishing of the wafer when the measured value of the current film
thickness, obtained from the optical film thickness measuring
sensor 60, reaches a predetermined value; transporting the polished
wafer to the wet-type film thickness measuring device 80 before
cleaning and drying the wafer; measuring the current film thickness
by the wet-type film thickness measuring device 80; calibrating the
optical film thickness measuring sensor 60 based on a comparison
between the measured value of the current film thickness obtained
by the optical film thickness measuring sensor 60 and the measured
value of the current film thickness obtained by the wet-type film
thickness measuring device 80; polishing a subsequent wafer having
the same structure; measuring the film thickness of the subsequent
wafer by the calibrated optical film thickness measuring sensor 60
during polishing of the subsequent wafer; and terminating polishing
of the subsequent wafer when the film thickness obtained from the
optical film thickness measuring sensor 60 reaches a predetermined
target value.
[0149] According to this polishing method, the optical film
thickness measuring sensor 60 is calibrated using the measured
value of the film thickness obtained by the wet-type film thickness
measuring device 80 that can carry out highly-accurate film
measurement. Therefore, an accuracy of in-situ film thickness
measurement that is performed during polishing of the subsequent
wafer can be improved. As a result, re-polishing of the wafer can
be eliminated. Moreover, the polishing conditions (including
polishing time and polishing pressure) that have been adjusted
based on the measurement result of the film thickness can be
applied to polishing of the next wafer. Therefore, the throughput
can be improved.
[0150] Next, the eddy current film thickness sensor 40 and the
optical film thickness sensor 60 will be described. FIG. 27 is a
schematic cross-sectional view showing the first polishing unit 3A
having the eddy current film thickness sensor and the optical film
thickness sensor. The polishing units 3B to 3D have the same
structure as that of the first polishing unit 3A shown in FIG. 27
and their repetitive descriptions are omitted.
[0151] The optical film thickness sensor 40 and the optical film
thickness sensor 60 are disposed in the polishing table 30A and are
rotated together with the polishing table 30A and the polishing pad
10. The top ring shaft 16 is coupled to a top ring motor 18 through
a coupling device, such as belt, so that the top ring shaft 16 is
rotated by the top ring motor 18. This rotation of the top ring
shaft 16 rotates the top ring 31A in the direction as indicated by
arrow.
[0152] The optical film thickness sensor 40 is configured to
irradiate the surface of the wafer W with light, receive the light
reflected from the wafer W, and break up the reflected light
according to wavelength. The optical film thickness sensor 40
includes an irradiator 42 for irradiating the surface, to be
polished, of the wafer W with the light, an optical fiber 43 as an
optical receiver for receiving the reflected light from the wafer
W, and a spectrometer 44 configured to resolve the reflected light
according to the wavelength and measure intensity of the reflected
light over a predetermined wavelength range.
[0153] The polishing table 30A has a first hole 50A and a second
hole 50B having upper open ends lying in the upper surface of the
polishing table 30A. The polishing pad 10 has a through-hole 51 at
a position corresponding to the holes 50A and 50B. The holes 50A
and 50B are in fluid communication with the through-hole 51, which
has an upper open end lying in the polishing surface 10a. The first
hole 50A is coupled to a liquid supply source 55 via a liquid
supply passage 53 and a rotary joint (not shown). The second hole
50B is coupled to a liquid discharge passage 54.
[0154] The irradiator 42 includes a light source 47 for emitting
multiwavelength light and an optical fiber 48 coupled to the light
source 47. The optical fiber 48 is an optical transmission element
for directing the light, emitted by the light source 47, to the
surface of the wafer W. Tip ends of the optical fiber 48 and the
optical fiber 43 lie in the first hole 50A and are located near the
surface, to be polished, of the wafer W. The tip ends of the
optical fiber 48 and the optical fiber 43 are arranged so as to
face the wafer W held by the top ring 31A, so that multiple zones
of the wafer W are irradiated with the light each time the
polishing table 30A makes one revolution. Preferably, the tip ends
of the optical fiber 48 and the optical fiber 43 are arranged so as
to face the center of the wafer W held by the top ring 31A.
[0155] During polishing of the wafer W, the liquid supply source 55
supplies water (preferably pure water) as a transparent liquid into
the first hole 50A through the liquid supply passage 53. The water
fills a space formed between the lower surface of the wafer W and
the tip ends of the optical fibers 48 and 43. The water further
flows into the second hole 50B and is expelled therefrom through
the liquid discharge passage 54. The polishing liquid is discharged
together with the water and thus a path of light is secured. The
liquid supply passage 53 is provided with a valve (not shown in the
drawing) configured to operate in conjunction with the rotation of
the polishing table 30A. The valve operates so as to stop the flow
of the water or reduce the flow of the water when the wafer W is
not located over the through-hole 51.
[0156] The optical fiber 48 and the optical fiber 43 are arranged
in parallel with each other. The tip ends of the optical fiber 48
and the optical fiber 43 are substantially perpendicular to the
surface of the wafer W, so that the optical fiber 48 directs the
light to the surface of the wafer W perpendicularly.
[0157] During polishing of the wafer W, the irradiator 42
irradiates the wafer W with the light, and the optical fiber
(optical receiver) 43 receives the light reflected from the wafer
W. The spectrometer 44 measures the intensity of the reflected
light at each of the wavelengths over the predetermined wavelength
range and sends light intensity data to the operation controller 5.
This light intensity data is the film thickness signal reflecting
the film thickness of the wafer W and varying in accordance with
the film thickness of the wafer W. The operation controller 5
produces a spectrum showing the light intensities at the respective
wavelengths from the light intensity data, and further produces the
film thickness index value representing the film thickness of the
wafer W from the spectrum.
[0158] FIG. 28 is a schematic view illustrating the principle of
the optical film thickness sensor 40, and FIG. 29 is a plan view
showing a positional relationship between the wafer W and the
polishing table 30A. In this example shown in FIG. 28, the wafer W
has a lower film and an upper film formed on the lower film. The
irradiator 42 and the optical receiver 43 are oriented toward the
surface of the wafer W. The irradiator 42 is configured to
irradiate the multiple zones, including the center of the wafer W,
on the surface of the wafer W with the light each time the
polishing table 30A makes one revolution.
[0159] The light, directed to the wafer W, is reflected off an
interface between a medium (e.g., water in the example of FIG. 28)
and the upper film and an interface between the upper film and the
lower film. Light waves from these interfaces interfere with each
other. The manner of interference between the light waves varies
according to the thickness of the upper film (i.e., a length of an
optical path). As a result, the spectrum, produced from the
reflected light from the wafer, varies according to the thickness
of the upper film. The spectrometer 44 breaks up the reflected
light according to the wavelength and measures the intensity of the
reflected light at each of the wavelengths. The operation
controller 5 produces the spectrum from the light intensity data
(the film thickness signal) obtained from the spectrometer 44. This
spectrum is expressed as a line graph (i.e., a spectral waveform)
indicating a relationship between the wavelength and the intensity
of the light. The intensity of the light can also be expressed as a
relative value, such as a reflectance or a relative
reflectance.
[0160] FIG. 30 is a diagram showing the spectrum created by the
operation controller 5. In FIG. 30, horizontal axis represents the
wavelength of the reflected light, and vertical axis represents
relative reflectance derived from the intensity of the light. The
relative reflectance is an index that represents the intensity of
the reflected light. More specifically, the relative reflectance is
a ratio of the intensity of the reflected light to predetermined
reference intensity. By dividing the intensity of the light (i.e.,
the actually measured intensity) by the corresponding reference
intensity at each of the wavelengths, unwanted noises, such as a
variation in the intensity inherent in an optical system or the
light source, are removed from the actually measured intensity. As
a result, the spectrum reflecting only the thickness information of
the upper film can be obtained.
[0161] The predetermined reference intensity may be intensity of
the reflected light obtained when a silicon wafer (bare wafer) with
no film thereon is being polished in the presence of water. In the
actual polishing process, the relative reflectance is obtained as
follows. A dark level (which is a background intensity obtained
under the condition that the light is cut off) is subtracted from
the actually measured intensity to determine a corrected actually
measured intensity. Further, the dark level is subtracted from the
reference intensity to determine a corrected reference intensity.
Then the relative reflectance is calculated by dividing the
corrected actually measured intensity by the corrected reference
intensity. That is, the relative reflectance R(.lamda.) can be
calculated by using the following equation (1).
R ( .lamda. ) = E ( .lamda. ) - D ( .lamda. ) B ( .lamda. ) - D (
.lamda. ) ( 1 ) ##EQU00001##
where .lamda. is wavelength, E(.lamda.) is the intensity of the
reflected light at the wavelength .lamda., B(.lamda.) is the
reference intensity at the wavelength .lamda., and D(.lamda.) is
the dark level at the wavelength .lamda. (i.e., the intensity of
the light obtained under the condition that the light is cut
off).
[0162] The operation controller 5 compares the spectrum, which is
produced during polishing of the wafer, with a plurality of
reference spectra so as to determine a reference spectrum that is
most similar to the spectrum produced. A film thickness associated
with the determined reference spectrum is determined to be a
current film thickness by the operation controller 5. The plurality
of reference spectra are those obtained in advance by polishing a
wafer of the same type as the wafer to be polished. Each reference
spectrum is associated with a film thickness at a point of time
when that reference spectrum is obtained. Specifically, each
reference spectrum is obtained at different film thickness, and the
plurality of reference spectra correspond to different film
thicknesses. Therefore, the current film thickness can be estimated
by determining the reference spectrum that is most similar to the
current spectrum. This estimated film thickness is the
above-mentioned film thickness index value.
[0163] The optical film thickness sensor 40 is suitable for use in
determining the thickness of the dielectric film having a property
that allows light to pass therethrough. The operation controller 5
may determine the removal amount of the film from the film
thickness index value (or the light intensity data) obtained by the
optical film thickness sensor 40. More specifically, an initial
estimated film thickness is determined from the initial film
thickness index value (or initial light intensity data) in
accordance with the above-described method, and the removal amount
is determined by subtracting the current estimated film thickness
from the initial estimated film thickness.
[0164] Instead of the above-described method, the removal amount of
the film may be determined from an amount of change in the spectrum
that varies in accordance with the film thickness. FIG. 32 is a
schematic view showing two spectra corresponding to a film
thickness difference .DELTA..alpha.. In FIG. 32, .alpha. represents
the film thickness. This film thickness .alpha. decreases with time
during polishing of the wafer (.DELTA..alpha.>0). As shown in
FIG. 32, as the film thickness changes, the spectrum moves along a
wavelength axis. The amount of change between the two spectra
obtained at two different times corresponds to a region (shown by
hatching) surrounded by these spectra. Therefore, the removal
amount of the film can be determined by calculating the area of
this region. The removal amount U of the film is determined using
the following equation (2).
U = .lamda.1 .lamda.2 Rc ( .lamda. ) - Rp ( .lamda. ) ( 2 )
##EQU00002##
where .lamda. is wavelength of the light, .lamda.1 and .lamda.2 are
minimum wavelength and maximum wavelength that determine the
wavelength range of the spectrum to be monitored, Rc is currently
obtained relative reflectance, and Rp is previously obtained
relative reflectance. The amount of change in the spectrum
calculated by the equation (2) is the removal index value
indicating the removal amount of the film.
[0165] Next, the eddy current film thickness sensor 60 will be
described. The eddy current film thickness sensor 60 is configured
to pass a high-frequency alternating current to a coil so as to
induce the eddy current in a conductive film and detect the
thickness of the conductive film from the change in the impedance
due to a magnetic field produced by the induced eddy current. FIG.
33 is a diagram showing a circuit for illustrating the principle of
the eddy current film thickness sensor 60. When an AC power supply
S (a voltage E [V]) passes a high-frequency alternating current
I.sub.1 to a coil 61, magnetic lines of force, induced in the coil
61, pass through the conductive film. As a result, mutual
inductance occurs between a sensor-side circuit and a
conductive-film-side circuit, and an eddy current I.sub.2 flows in
the conductive film. This eddy current I.sub.2 generates magnetic
lines of force, which cause a change in an impedance of the
sensor-side circuit. The eddy current film thickness sensor 60
measures the thickness of the conductive film from the change in
the impedance of the sensor-side circuit.
[0166] In the sensor-side circuit and the conductive-film-side
circuit in FIG. 33, the following equations hold.
R.sub.1I.sub.1+L.sub.1dI.sub.1/dt+MdI.sub.2/dt=E (3)
R.sub.2I.sub.2+L.sub.2dI.sub.2/dt+MdI.sub.1/dt=0 (4)
[0167] where M represents mutual inductance, R.sub.1 represents
equivalent resistance of the sensor-side circuit including the coil
Q, L.sub.1 represents self-inductance of the sensor-side circuit
including the coil Q, R.sub.2 represents equivalent resistance of
the conductive film in which the eddy current is induced, and
L.sub.2 represents self-inductance of the conductive film through
which the eddy current flows.
[0168] Letting I.sub.n=A.sub.ne.sup.j.omega.t (sine wave), the
above equations (3) and (4) are expressed as follows.
(R.sub.1+j.omega.L.sub.1)I.sub.1+j.psi.MI.sub.2=E (5)
(R.sub.2+j.omega.L.sub.2)I.sub.2+j.omega.MI.sub.1=0 (6)
[0169] From these equations (5) and (6), the following equations
are derived.
I 1 = E ( R 2 + j.omega. L 2 ) / [ ( R 1 + j.omega. L 1 ) ( R 2 +
j.omega. L 2 ) + .omega. 2 M 2 ] = E / [ ( R 1 + j.omega. L 1 ) +
.omega. 2 M 2 / ( R 2 + j.omega. L 2 ) ] ( 7 ) ##EQU00003##
[0170] Thus, the impedance .PHI. of the sensor-side circuit is
given by the following equation.
.PHI. = E / I 1 = [ R 1 + .omega. 2 M 2 R 2 / ( R 2 2 + .omega. 2 L
2 2 ) ] + j.omega. [ L 1 - .omega. 2 L 2 M 2 / ( R 2 2 + .omega. 2
L 2 2 ) ] ( 8 ) ##EQU00004##
[0171] Substituting X and Y for a real part (i.e., a resistance
component) and an imaginary part (i.e., an inductive reactance
component) respectively, the above equation (8) is expressed as
follows.
.PHI.=X+j.omega.Y (9)
[0172] The eddy current film thickness sensor 60 outputs the
resistance component X and the inductive reactance component Y of
the impedance of the electric circuit including the coil 61 of the
eddy current film thickness sensor 60. These resistance component X
and the inductive reactance component Y are the film thickness
signal reflecting the film thickness and vary in accordance with
the film thickness of the wafer.
[0173] FIG. 34 is a diagram showing a graph drawn by plotting X and
Y, which change with the film thickness, on a XY coordinate system.
Coordinates of a point T.infin. are values of X and Y when the film
thickness is infinity, i.e., R.sub.2 is zero. Where electrical
conductivity of a substrate can be neglected, coordinates of a
point T0 are values of X and Y when the film thickness is zero,
i.e., R.sub.2 is infinity. A point Tn, specified by the values of X
and Y, moves in a circular arc toward the point TO as the film
thickness decreases. A symbol k in FIG. 34 represents coupling
coefficient, and the following relationship holds.
M=k(L.sub.1L.sub.2).sup.1/2 (10)
[0174] FIG. 35 shows a graph obtained by rotating the graph in FIG.
34 through 90 degrees in a counterclockwise direction and further
translating the resulting graph. As shown in FIG. 35, the point Tn,
which is specified by the values of X and Y, travels in a circular
arc toward the point T0 as the film thickness decreases.
[0175] A distance between the coil 61 and the wafer W changes in
accordance with a thickness of the polishing pad 10 that exists
between the coil 61 and the wafer W. As a result, as shown in FIG.
36, the arcuate path of the coordinates X, Y changes in accordance
with the distance G (G1 to G3) corresponding to the thickness of
the polishing pad 10. As shown in FIG. 36, when points specified by
the components X and Y at the same thickness of the conductive film
are connected by lines (which will be referred to as preliminary
measurement lines) with different distances G between the sensor
coil 61 and the wafer W, these preliminary measurement lines
(r.sub.1, r.sub.2, r.sub.3, . . . ) intersect each other at an
intersection (a reference point) P. Each of these preliminary
measurement lines m (n=1, 2, 3 . . . ) is inclined at an elevation
angle (included angle) 0 with respect to a predetermined reference
line (e.g., a horizontal line H in FIG. 36). This elevation angle
.theta. varies depending on the thickness of the conductive film.
Therefore, the angle .theta. is the film thickness index value
indicating the film thickness of the wafer W.
[0176] During polishing of the wafer W, the operation controller 5
can determine the film thickness from the angle .theta. with
reference to correlation data showing a relationship between the
angle .theta. and the film thickness. This correlation data is
obtained in advance by polishing the same type of wafer as the
wafer W to be polished and measuring the film thickness
corresponding to each angle .theta.. FIG. 37 is a graph showing the
angle .theta. that varies with the polishing time. Vertical axis
represents the angle .theta., and horizontal axis represents the
polishing time. As shown in this graph, the angle .theta. increases
with the polishing time, and becomes constant at a certain point of
time. The operation controller 5 calculates the angle .theta.
during polishing and determines the current film thickness from the
angle .theta..
[0177] The above-described optical film thickness sensor 40 and the
eddy current film thickness sensor 60 may be a known optical sensor
and a known eddy current sensor as disclosed in Japanese laid-open
patent publications No. 2004-154928 and No. 2009-99842.
[0178] As shown in FIG. 4, in addition to the optical film
thickness sensor 40 and the eddy current film thickness sensor 60,
the torque current measuring device 70 is provided for measuring
the input current (i.e., the torque current) of the table motor 19
that rotates the polishing table 30A. The value of the torque
current measured by the torque current measuring device 70 is sent
to the operation controller 5, which monitors the value of the
torque current during polishing of the wafer W. Instead of
providing the torque current measuring device 70, a current value
outputted from an inverter (now shown) for driving the table motor
19 may be used for monitoring the torque current.
[0179] The principle of the film thickness measurement carried out
by the wet-type film thickness measuring device 80 shown in FIG. 6
is the same as that of the above-discussed optical film thickness
measuring sensor 60, and its duplicative descriptions are omitted.
FIG. 38 is a schematic view showing details of an optical film
thickness measuring head 42 of the wet-type film thickness
measuring device 80. As shown in FIG. 38, the optical film
thickness measuring head 42 includes an irradiator 142 configured
to irradiate the surface of the wafer W with light, an optical
receiver 143 configured to receive the light reflected from the
wafer W, a spectrometer 144 configured to break up the reflected
light according to wavelength and measure intensity of the
reflected light over a predetermined wavelength range, and a
processor 150 configured to produce a spectrum from light intensity
data (film thickness signal) obtained from the spectrometer 144 and
determine a film thickness based on the spectrum.
[0180] The irradiator 142 includes a light source 147 for emitting
multiwavelength light. The irradiator 142 and the optical receiver
143 are located adjacent to the transparent window 90 and oriented
toward the wafer W held by the holding device 82 (see FIG. 6A and
FIG. 6B). Preferably, the irradiator 142 and the optical receiver
143 are oriented toward the center of the wafer W held by the
holding device 82.
[0181] The previous description of embodiments is provided to
enable a person skilled in the art to make and use the present
invention. Moreover, various modifications to these embodiments
will be readily apparent to those skilled in the art, and the
generic principles and specific examples defined herein may be
applied to other embodiments. Therefore, the present invention is
not intended to be limited to the embodiments described herein but
is to be accorded the widest scope as defined by limitation of the
claims and equivalents.
* * * * *